It is unlikely that the nail will suddenly change in composition. If it did, it would take months before the new composition dominated the nail plate, since the nail's composition is mostly determined in the matrix.
I hear what you're saying.
Here's an example.
Client no#1 has been coming for 3yrs. For 1.5yrs, she has had UV Gel, and suffered ZERO lift. She was very diligent with her oil and bought new oil regularly.
Suddenly she had lift.. everywhere and AWFUL.
I asked "what's new? what changes have you made? what have you been doing/using lately?"
She could think of nothing.
A couple of weeks later, she was at her Doctor's office.
He noticed the dreadful lift on her nails. He said to her "are they uv gel?" and she looked at him surprised and said "yes, how did you know?" (because really?? a doctor knowing about this stuff? not very common)
He said "my wife was wearing them too until she started her anti-depressants, now she can only wear acrylic. Uv Gel won't stick".
My client called me that afternoon, to tell me of her appointment and to apologize because she had started her anti-depressants a few months ago and didn't think to mention them when her lift had started a few months later. Not realizing that, AS YOU SAY, the effect would take time to reach the nail plate...
Now, she wears L&P and has zero problems. Granted, she is able to wear L&P and she's not one of those that can't wear anything.
BUT I'm just wondering what exactly those anti-depressants did to her nailplate?