Hi. I've just bought this Heuer 844 and I'm hoping to verify its authenticity

Hi. I just bought this 844 online and I'm concerned it's not right. Can anyone advise. After a bit of research I feel the case back is not correct and there should be a serial number there and 844 stamped. Could the back be original? it has Heuer signed on the inside. `could the serial number have been polished out? I also feel the lume hasn't aged correctly for a 40 year old watch. I would be very greatful for any opinions. Probably should have asked these questions before buying🙃 Many thanks. Nick

Hi. Many thanks for your input. I really appreciate it. Posting a pic of the inside of the case. Is the caseback not being original a major issue ? this would obviously effect the value? The seller claims that some casebacks were made in Switzerland and some in France for this model?all the best. Nick

So the watch itself is probably the early French version or the face at least and the caseback Swiss. This is a mismatch as the correct caseback should be the French made Monnin? I bought it on Chrono24 so could probably get refunded. Many thanks. Nick