Hi Dan,
concerning your violin. It may be very hard to find out who actually built it. It is not an original Guarnerius, but was most likely made in Saxony/Bohemia. The Letters on the violin's back are in my opinion not related to the one who built or repaired it. So they could be anything- an R for sure, and a J or G (I read a G there) or even a Y. They were most likely -as Udo already stated- a scratch made to link this instrument to a former owner. Neither for the origin nor the value of the instrument these letters are relevant. So forget about them.
According to the Gläsel label inside: this could be the label of the repair or of the violin's origin. What gives you the idea, that Gläsel did not repair "copies"?
1. Clearly, the position of the label is near the old repair. If e.g., the luthier did not open the Instrument completely to do the repair, putting the label on the neck base may have been an obvious solution as removing the neck was necessary for repair anyway.
2. The Gläsel factory was a company, not a single luthier sitting lonely in his workshop, being a nerdy genius deciding to dedicate his live to precious violins only

On the contrary: These large workshops often offered a wide range of products, cheap and expensive violins, used and new violins, repairs and service, spare parts.... And like today, they repaired everything a customer was willing to pay for. But your violin is of good quality, so this repair was totally justified, and not a bit unjustified or remarkable. So nothing crazy there either.

The origin of the violin: This is most likely a saxonian/bohemian instrument. At that time, both these regions were not only geographically linked, but held very close production and trade relations. The large manufactures exchanged instrument parts, and bought violin parts as well as white instruments as well as completed violins from small workshops and poor homeworkers, selling them under their own name/brand. So even IF the label of Gläsel is the one the violin originated, you will never find out who exactly made it. Whether it was made in the workshop, or whether it was one of the instruments only traded there is not traceable any more. Only in very occasional cases, a violin from these large manufactures has so distinct characteristics. Did you know, that around 1900 the US had a consulship/specialized embassy in Markneukirchen, ONLY for organising the trade with musical instruments? The amount of instruments produced and traded there was enormous at that time!
Value of the violin: The large manufacturers sold a lot of different violins in different qualities. They bought master instruments from smaller workshops and single luthiers, produced master instruments by themselves, and produced cheaper instruments for beginners and families. And often all of them bear similar labels. To judge the value of an instrument just by a photo (or a few...) is simply not possible. One may get a somehow estimated value if the instrument is definitely a genuine one of a known maker, but for most of the instruments this is not the case. For your instrument, it may come from Gläsel or not. For the value this is not important, as Gläsel had cheaper and better instruments, and a violin without any label may be better than one with label.
For estimating a violins value, the sound of the instrument is extremely important. Furthermore, one must take the repairs into account. Basically, you may want to cover the violin's value with an insurance. The insurance amount should cover the sum necessary to get an equivalent instrument. Therefore, the value of the instrument is relative to your local market situation, which may change over time. Someone judging the violin's value therefore must know a bit about the prices of violins of similar sound quality. And no insurance is able to cover the individual family value of the insurance. No other violin will be the one your ancestors played except this one, and no other violin will hold these memories for you.
So I suggest that you ask your local luthier for a value appraisal. And yes, trying to find out about the history of an instrument is interesting and fun. But I suggest that you extend the radius to the general history of instruments and their makers in Saxony and Bohemia- the way these instruments were made, the way the trade involved and changed over time, the way the poor small workshop luthiers suffered by the price dictators (big manufacturers), and how families had to survive under very poor conditions. It may give you -at it did for me!- a lot more respect and a very different idea of the value of the "cheap manufacture instruments at Ebay". And if you come to Germany, visit the Markneukirchen Museum!