By now, most people would have heard of the "Yusok Ishak" gaffe. For the uninformed, it was an embarrassing mistake made by the Monetary Authority of Singapore in the recently launched SG50 commemorative note sets.

The name of Singapore's first President, Mr Yusof Ishak, was misspelled twice on the packaging - on the cover fold and enclosed booklet - though the commemorative notes did not contain errors.

Besides highlighting the fallibility of proofreaders, the blunder has prompted speculation that the value of the set would rise. Reports stated that some people were trying to sell the packaging without the notes, saying that the folders themselves are "limited edition".

People should hold their horses, say banknote, coin and stamp dealers whom Life interviewed.

Yusok-gate is not going to make a collector's item out of these note sets for two reasons.

First, the mistakes appeared on the packaging and not the notes themselves.

Second, the error was widespread and not limited to only a small handful of folders.

Says Mr Laurence Lau, 59, owner of coin-and-banknote dealership Coins & Coins: "Since everyone has the same thing, the mistake becomes a standard deviation. The value of the set does not go up."

The same can be said even if the error had occurred on the notes. If all the notes had the same problem, this could raise their value, but it would not be by much.

However, if only a very small percentage of these notes were affected, the value could rocket to "easily 10 to 20 times above value", says banknote collector Nat Toh, 29.

For other types of errors, it could be hard for a layman to discern if the error can increase the item's value, but dealers will know.

Mr Leon Lee, 53, manager of coin-and-banknote dealership Monetarium Singapore, has been in the business for 22 years.

This is his tip: "The harder it is to explain an error, the higher the value of the item is likely to be."

He explains that if even the dealer cannot figure out how the error came to be, the mystery surrounding it adds to its uniqueness.

Whether an error can boost the value of a note, coin or stamp also depends on the demand for the item and the amount the buyer is willing to pay.

"It's not a commodity which has a market price," says Mr Toh, who works as a commodities trader and has been collecting banknotes since the age of 12.

"Since supply is limited, a very keen collector could raise the value of the note he has in mind."

Banknote and coin errors typically occur during the printing and minting processes.

Common banknote errors include wrong or mismatched serial numbers, missing colours that could be a result of the printer running out of a certain colour of ink, and gutter folds - a misprint that happens because the sheets are crumpled when stamped upon.

Apart from print errors, there are mistakes of another sort, which experts here classify as cutting errors. These could leave the notes with an extra "fin" - an extra corner or edge or, in some cases, a piece of paper attached to the note.

While the paper can be easily torn off, those who chance upon such notes usually know they are onto something special and leave the attachment untouched.

Mr Lau says he recently came to know of an owner of such a $1 note, who was offered $1,000 by a collector. The owner refused to part with the note, though, because of sentimental reasons.

Coin errors can arise when they are minted on metals of the wrong thickness from others in the lot, which leads to misalignment.

Mr Lee says he has encountered cases in which the wrong metal was used. For instance, a coin that was to be minted on copper nickel finds its way onto silver instead.

Stamp errors are known to philatelists as "varieties", says the Singapore Philatelic Museum spokesman. "Although you might reject error stamps due to their imperfections, they are considered a collector's item," he adds.

Stamp errors that happen because of printing mistakes could include a missing colour or image, an inverted image, and a missing or misaligned perforation.

There are also errors that occur during the design process that result in spelling mistakes, the use of a wrong word, or inaccurate representation of subject matter.

Industry experts say these coin, note and stamp errors were more prevalent in the past.

But with the improvement of printing technology, errors have become few and far between.

This makes it possible for those who own or come across errors to command a premium for them.

Mr Tan Chun Lim, 70, who owns stamp dealership CS Philatelic Agency, was recently informed of what he terms a "modern error" in a stamp from SingPost's 2008 stamp issue.

The original Peranakan-influenced stamp, which is hailed as the world's first beaded stamp, comes with a collector's sheet in the shape of a purse. The stamp features a deer. The error stamp, however, shows the animal upside down.

Mr Tan says this is one of the "best" errors he has ever seen in a modern stamp.

He managed to close a transaction for a five-figure sum last week. The price of the collector's sheet was $8 at the time of its release.

Collectors and dealers alike say the scene for transactions of notes, coins and other collectibles here is a robust one.

There are three auction houses here for coins and notes, says Mr Lim Beng Haw, 69, owner of Taisei Stamps & Coins dealership.

He estimates that there are more than 50 dealers in the scene and over 20,000 serious collectors.

The auction houses have close to 10 auctions a year, although errorrelated pieces that are put up for auction are very rare.

Mr Lee of Monetarium Singapore is getting ready for an auction in October, which will see more than 1,000 items put up for bidding.

Out of these, however, only three items are error-related.

"It's not good if there are too many errors in circulation. It means there's a problem with our printing process and quality control," he says.

Mistakes or otherwise, this appears to be a thriving business.

"You know why? The bottom line is money," says Mr Lim.