First Strike Coins Perth Mint

I am assuming you are referring to graded coins, it's a designation for coins within the first month of release and says so on the label. Generally it does carry some premium though that varies how much from issue to issue.

Sometimes a coin that was struck within the first 100, on the first day of production, is indistinguishable in strike quality from an example that was struck 60,000 examples later.

I visited the Royal Australian Mint in Canberra, where they had a Public coin operated minting press. You put a Two Dollar coin the the slot, and out comes a fresh from the dies One Dollar coin. I was completely unaware that on the day I turned up, just after opening to the Public early in the morning, that fresh unused dies had been installed in the press. I found out about two years later.

I have examples from both ends of the run of about 60,000, and I cannot detect any difference in strike quality.