How to access my syscoins bought in 2017 which I placed in a blockmarket wallet?

I bought some syscoins in 2017 and transferred them to a blockmarket wallet. Today, I checked my public address on a sys explorer but it can’t find the address. I tried to follow this guide Blockmarket or Syscoin 2/3.x.x to Syscoin 4.x.x — Upgrade Guide, but I don’t have blockmarket on my computer anymore. I can’t remember the version I previously used also. So I downloaded the latest version of Blockmarket Blockmarket 3.2.0 and installed it. I found Import wallet but I don’t have any .dat file. I only stored the private key of my address. How can I gain access to my syscoins?

If you have the private keys you can just import them onto 4.1.3, go to the console and type
importprivkey “privkey”
privkey being your private key

I got null when I do importprivkey. Anyway, why can’t I find any search results when I searched for my address in the explorer?

Null is the correct response, are you able to let me know what the address is you think you should have Sys in

I realised I remembered wrongly. I checked my transaction records in my exchange and found that I did not transfer the syscoins out. However, I did create a wallet with address 12U9hVr1wLTqyrNWEA5TFCNAmjECWkqSrU. Why can’t I find any search results when I searched for my address in the explorer? And how do I check whether the wallet I imported has the mentioned public address?

Sys changed its address structure in SYS3 from BTC type to S type you can see your S address here

So 12U9hVr1wLTqyrNWEA5TFCNAmjECWkqSrU changed to SNm9jLdAfhf3WA9xmb4Xo6WjRWTdMzURKu so your SYS4 wallet should have this address

If you have never used an address it will not show anything in the explorer

Yes I found it in the receiving addresses. I saw a few other addresses with no label and 1 labeled home. What are those?

Have no idea not knowing your history back then, it really does not matter now as you never sent any coins to any address. If you are concerned just create a new address and you should also have made a copy of your wallet.dat once you have encrypted it