Searching a specific trade through golds logs is sometimes time consuming especially when you pause away d2jsp from time to time.
Example 1 :For my account, I have actually 124 entries in the select. Let's say I did one trade in april 2012, two in 2014 (may and june) and one more in september 2016 and nothing else. Checking the checkbox would allow me to have only four entries in the select box and I would browse gold logs way faster.
Example 2 :An old user who comes a couple of months on d2jsp every years and wants to check on a very old trade. The trade could have happened in 2007, 2008, 2009 or even early 2010.
He would have to check his gold history for ~36 months. And what if he was mistaken and the trade was in fact in early 2011 ? that would be ~12 months to checks.
Proposition :So my suggestion would be to add a simple checkbox, by default unchecked, like in this screenshot (obviously design is a little crap, sorry) :

and when clicking on the checkbox it would makes an AJAX call repopulating the select with only months where there is at least one entry.
The point is also, that as long the checkbox is not used, there is no need to change a single thing , so this is litteraly just a feature add with no breaking changes