Potential collectors item

Earlier this year the Royal Mint put into circulation another edition of the 20 pence coin, but unfortunately they had not realised that there was an error. On one of the sides of the coins there should have been a date displayed, but unfortunately this was left off (see article), the result being that thses coins were now sought after and considerably more value than the tendered value of 20 pence. This got me thinking about the new 500 peso bill in the Phillipines that has been published (see article). Should I put an order in now? Are there any other blunders that have increasded the value of other products?