Until today, my last communication with the manager of FTDNA Kit Number 471827 was in August 2019. This sample did Big Y and was positive for a prolific line of J2b-Z631>Z1043 known as J2b-CTS11760.
His uniparental male line ancestor was Joakim von Holtz who had died in Eskiltuna, Sweden in 1669 after having migrated there from some unknown part of Germany.
Because the living descendant has two mutations in his first 12 STRs from what the J2b-CTS11760 ancestor had, who lived 2600 years ago by YFull estimate, he doesn't get any matches within the FTDNA database. YFull calculates these ancestral haplotypes in the "info->STRs" tab.
We were disappointed that his Big Y didn't result in a new branching point below J2b-CTS11760. Instead, it indicated that he was equally distantly related to all J2b-CTS11760 men.
Closest relative from an unlikely GD 3/12 Match
Yesterday I found that a man in the J2 public project along with a man in the Glantz project are likely to be von Holtz's closest male line relatives.
So far all I know about these two men is what they made publicly available - one man traces his male line to an ancestor named Heironymus Glantz from somewhere in Germany.
Apart from matching the von Holtz descendant on four reliable rare alleles, he has the DYS485 15 to 17 mutation, an indicator that he is positive for J2b-Z8429, the immediate parent of J2b-CTS11760 on YFull. So we already know he must be restricted to that portion of the tree.
I hope one of these men will eventually do a WGS or Big Y test and establish the SNPs defining this male line on the YFull tree, if my prediction based on the STRs is correct.
Roman-mediated migration from the western Balkans or surrounding areas to the Upper Germanic-Rhaetian Limes is definitely one possible vector for how their ancestor(s) may have migrated to Germany.
I'll be happy to go into more detailed speculation once their branch is on the YFull YTree with an age estimate.