Hi Sue1972 - worry not. Oestrogel is oestrogel even if it is sometimes given a different name for different markets - this is the same for some other HRT products. Why they are given different names in different countries is beyond me, but only serves to worry women unnecessarily! They cannot be different in the sense that they are made to the same formulation by the same company and crucially also the same concentration of estradiol - they have to.
It absolutely CANNOT be made weaker due to the shortages - the amount of estradiol per g of gel will be the same in all bottles of oestrogel made by Besins and they would not change the dosage without declaring it. Do be assured of that.
I would suggest that gel is more likely to give rise to differences in absorption - if there are any and as Tinkerbell says - weather changes will definitley make a difference. Absorption is very much affected by temperature of the skin, and to some extent the temperature of the bottle - warmer weather may make it slightly runnier. Possibly also a bottle that has been opened sometimes may end up runnier towards the end - I certainly found that with testogel (same formulation except for active ingredient). What else you put on your skin (eg shower creams, body creams etc) also will affect absorption too as well as where you apply it.
There has been a lot of discussion around bottle shapes, names, coloured squares, you name it - differences in any of these things have been said to cuase differences in absorption. Some say more some say less - but the same product can't be both weaker and stronger at the same time!
So far there is no evidence, beyond anecdotal, that it has anything to do with the gel per se, but most likely something else. If there was proper evidence - then I will revise that view but until then - let's go with the most likely explanation and above all NOT TO WORRY!
Why I'm saying all this is that the most important thing for you, is that you are taking HRT, it's a very effective HRT, and I urge you to continue with it and focus on the fact that it is going to work and make you feel better. If you feel your symptoms have (consistently) returned for whatever reason - say over a period of several weeks, then perhaps you need an extra half pump as you suggest - so why not give this a try and mention to your doc.
Yes as you say - it is most likely to be just coincidence - only placebo controlled trials would show anything - if there was something to show.
All the best and hope your symptoms resolve soon

Hurdity x