the 6263 produced between last 3.950.000 and 4.137.000 are in that period can be dial :
Sigma NO DAYTONA ,
SIGMA + DAYTONA ,
Only DAYTONA without Sigma ....( only between 4.137 and 5.5)
because is the period of change dial ....
i think production period is for 70% produced in 74 and 30% probably later
but people often believe 77, because also if produced in Rolex before ,
often consigned to the shop 6/12 months later and often not sold , but sold years later ..
So probably many peoples confuse date of warranty sold in shop with date of real production in factory