Rick,
Hi, no I would say that is not the case about having a surname you trust. The idea is it gives you clues that you can research around.
I have 9 matches, on me and one other share a variation of the same surname. But this tells us that our surname or variant was in use by the family before 1650 or so.
It gives some clues as to where we should look further.
Hopefully in time we will get more matches.
So back to your situation. Just to clarify things. So you are looking at your mothers family. So you got a male sibling, cousin, uncle or her father to do the YDNA test?
With regards your match. Looking at the information provided by FTDNA for your haplogroup.
We get :
Your haplogroup appeared between 1200 and 1750 with a most likely of about 1500.
As you say there is a link to the Aminoff family.
Wikipedia says there are three branches, of which the Russian Branch is extinct.
This may not be correct. It is simply that the family that there are records of are extinct.
FTDNA suggests joining the Swedish group as here and Finland are where the known family members are currently and so you might be able to work out your ancestor more easily.
However this is more a waiting game.
You mention sadly that your match has died which is sad, but the link may have been before most records given the proposed date of origin of your haplogroup.
I would recommend progressing with your Autosomal data with MH.
The first thing is to make your tree as big and wide as you can.
Cousins, 2 cousins etc. the bigger the tree, the easier it is to start to make sense of the groups from the next step.
Also you are providing the MH system more data to find links.
Now start grouping matches using labels.
Starting with you closest match give them a label, then use that label to tag the people who are shared DNA matches.
Repeat with the next closest match who is not in this group.
And so on.
Once you have say 8 groups you need to start looking at any trees they have and see if you can link those trees, you don’t need to absolutely link them, location may give pointers, so I have some of my unknown groups labeled, Scotland and Licolnshire, England.
Once you have started this process you can expand it to more groups.
Hopefully once you start this process you will be able to start assigning matches to each parent and grandparents line.
Obviously you make this simpler if you start with your mothers family Autosomal DNA, you are halving the number of family matches.
This is the method I use myself.
There are many, one of the best known is what is called the Leeds method.
I suggest you do some research into this and DNA genealogy more widely, it is not a silver bullet.
Have you generated an MH Autocluster? This automatically does something like I have described, but is not so useful with smaller matches.
Finally do not despair with smaller matches, I have made contact with and built trees linking people who I have 10cM / 5th - 6th cousin matches.
This has ended up being slightly longer than I had anticipated, feel free to ask for clarification, or PM me.
Happy Hunting
