Back in the day when the gun was made, the prevailing attitude was, if you want your gun to be drop safe, don't drop it with a loaded chamber.
I talked to my Colt guru about your question, and he never heard of any change to the firing pin. The pocket 1903 DID have a change in the slide during production, but it had to do with barrel retention. The expert in older guns we had for a gunsmith back in the dark ages, told him about it, and said, if you're trying to get a barrel, it will be the wrong one for the slide you have...
Never any mention of any change to the firing pin. SO, I'd call BS on the guy who told you they did, unless he has references from Colt.
Just FYI, don't trust any half cock notch to make your gun drop safe. Most of them won't. The are intended to catch the hammer if you slip while cocking it, not survive the gun landing on them.
Sorry I can't be of more help. Good Luck!
(personally, I wouldn't worry about it, get a quality holster for carry, and don't drop it!
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