I think t_solo_t is not an active member, so for the records here is a copy paste from his today's Instagram.

"t_solo_t Mystery solved Blue bezel 300 after considerable help from a knowledgeable collector the mystery is solved There is a small batch at the end of the line of the 300 which went primarily to South Africa with 2 others to Asia which has this genuine blue cast to an original bezel which is Tritium and Acrylic...the insert is original not from a similar Seamaster.. it’s rare 9 known"

 

"the insert is original not from a similar Seamaster"

My guess: as that blue insert is exatcly the same as a 166.073 "deep blue", they probably put a wrong insert in a batch of 165.024 bezel and delivered the far enough not to get any complain !!

 

Thank you so much for this info! I was really worried and loss some sleep trying to get more info on the blue bezel on the SM300. Yes, it appears to be this “genuine blue cast to an original bezel which is Tritium and Acrylic” because when I put the watch under the lamp for a few seconds and switch the lamp off the backlit bezel glows in the dark like other Seamaster 300s’ bezel. The one that I acquired recently was from Asia which the seller/watchmaker had asserted to me that the bezel and insert are original.