Hi Steve, I disagree about answering my own question,though I understand what you mean.
As we all know, there were many different manufacturers of all types of aircraft components during WW2 (a strategy that governments employed to try and minimise the risk of supply interruptions should a factory be bombed and to increase production cspacity). But as a result, sometimes a component from company A differed slightly from the identical component from company B.
Alternatively, sometimes a component underwent slight changes in design during its production lifetime ( Bf109 canopy frames for example). This would make the use of a certain style of part more appropriate for a specific period.
I'm sure that the above is the case with Luftwaffe drop tanks too.
I'm trying to establish if it is a known or documented phenomenon that some 300l drop tanks had a tube at the front and others of identical type didn't, and if so, was it due to being made in different factories or simply being made at different times during WW2.