I believe it was Marc Savoy who probably was the first builder in Louisiana, to use screws to hold the reed plates. I know Sidney Brown didn't use them, nor did Charlie Ortego. In the the beginning, Marc was using the screws to hold the reed plates on a bed of felt or leather. There was no wax at all. At some point, he abandoned the idea of the felt/leather, and started using wax to seal the plate, but still uses the screws.
Yes, the screws are an added "insurence" against the plates falling out of place, but they are time consuming to deal with. I didn't used to put them in on my accordions. I had heard all sorts of reasons why Marc was screwing the reeds down. Some one told me that it made a difference in the sound of the reeds.
So...... I did a little experiment of my own. On the next accordion I built, I installed the reeds as usual, wax, no screws. I tuned the reeds. I played the accordion. I listened to the tone and overall sound. I then installed screws . I played the accordion. I listened to the tone and overall sound.
Absolutly no difference what so ever.
A good friend of mine asked me to install the screws on one of his accordions ( Magnolia ) because he thought he get more volume from it. Same result, no difference. The only conclusion I could come to is, the screws serve only to help hold the plates in place.
A good idea if the accordion is to be shipped, so I do use them on my accordions now.

Jude

Screws and small nails had been used on all types of accordions and concertinas in the past dating back many years. However now it seems that even on high quality professional piano accordions wax does the job.