How to fill row based on multiple criteria with the most recent of multiple matches

Hi All,
This is my first post, though I have used the site in the past and it has saved my a** countless times. So thanks for that. Anywhosle, I have a problem that I thought I had solved by reading other posts, but I ran into a hiccup that I cannot overcome and has been frustrating me for weeks.
At work I have to take samples and distribute them to people, then log a bunch of information every time, which means I need to manually look up multiple pieces of information from multiple sources and it's just taking too long. To fix this I created a MATCH INDEX Formula (I do not have it on me or in the attached example sheet now, but I can find it on Tuesday when I'm back at work) that fills in a sample name into column C by looking for values for both columns A&B of the same row in the the entire sheet.

(Please see the attachment)
The main problem I am having now is that when there have been multiple aliquots of the same sample, the INDEX MATCH function will only look up the first value it comes across, which is causing it to return the incorrect value for 'amount remaining'. What I need is a function that can do the index-match magic for the MOST RECENT of the multiple values.

A second problem that I have not even begun to figure out is that since I have multiple sets of the same sample (i.e. duplicate, & triplicate for some), I need a function that can search (sequentially) the "Sample Log" sheet, then the "Sample Duplicate List" sheet, and finally the "Sample Inventory" sheet for matching values corresponding to the typed-in box & position. This would be SO helpful, but to me it sounds like it might be too complicated for practical use in excel, so I do not have high expectations for this second part.

Thank you very much for taking the time to read & (hopefully) help me solve this thing!

Dilipandey- For example, the output in F14 with my current formula would be 200 (from cell H2), but I would want it to output the value in cell H10 (100) because that would be the "current" amount of sample left.

Thank you very much! That is precisely what I was looking for!