When did Wagner Ware switch to a 4 digit part number

[Valerie Johnson]

When did Wagner ware switch from a single digit number/letter part number to a 4 digit part number letter and di the switch coincide with the switch in handle styles , specifically the early handle with a reinforcing rib to the later handle with the ground flat triangular spot.

By single digit part number/letter I mean for example like 6c and by 4 digit part number/letter I mean like 1056H, Both are no.6 skillets and both have the stylized high Wagner Ware Sidney -O- mark but are significantly different skillets, Is there a definitive date or period when they changed or did they overlap, I know the outside heat ring skillets start earlier than the smooth bottom skillets

[Roger Barfield]

I believe they changed in 1924. 

[Valerie Johnson]

Hi Roger, The stylized Wagner Ware Sidney -O- high mark started in 1924 on skillets with a heat ring so would that mean that there was only 1 year where skillets with the older style handle and single number with letter  overlapped skillets with the newer style handle and 4 digit part number/letter or was Wagner inconsistent and ran batches of the 2 different styles together