Acrylic crystal question

[WatchFanZac]

Hi all,

I have discerned from posts here that among vintage Rolex cognoscenti there is a preference for "original" acrylic crystals over "service replacement" acrylic crystals. While I totally understand the desire to keep a vintage watch as original a possible when it relates to dial, bezel and hands etc I don't fully see how this applies to crystals.

Is there an observable difference between service crystals and the ones the watches had when they left the factory? Have they a different thickness? Are they made from a more modern material that changes their appearance?

If there is no observable difference then haw does one know if the crystal is original or service?

Thanks for your patience I am (relatively) new to vintage Rolex after years as a vintage Omega fan.

Regards,

Zac