Horizons Premiership winners Wanganui City decided they couldn't sustain the step up, and Taranaki Premiership champions New Plymouth Boys' High School were losing 11 or 12 Year 13 players from their squad.
Neither the Horizons nor Taranaki league runners-up had signalled an intention to seek promotion, and Thistle's record of two close second-place finishes in the past two seasons showed they had the on-field consistency to go with their well-established and functional club base, Blair said.
This year the Federation League was a nine-team competition won by New Plymouth Rangers, who had former Gisborne Thistle coach Matt Hastings in their line-up.
Blair said it was not clear yet whether New Plymouth would go up a level to the Central League, but Hastings was taking over the coaching reins for next season and it would be an interesting meeting if he was in charge for a visit by Rangers to his old club in Gisborne.
Federation League bottom team Levin would not be relegated, and Thistle would come in as the 10th team.
“We believe we will get a draft draw at the end of this month,” Blair said.
“That would give us the time to start looking at travel and costs.”
As things stand, the Federation League next year would comprise: New Plymouth Rangers, Wanganui Athletic, Palmerston North Marist, Havelock North Wanderers, Massey University, Red Sox, North End, Napier Marist, Levin and Gisborne Thistle.
Thistle last played in the Central Federation League in 2017, when they finished fourth out of seven teams. Their coach then was Hastings, who was succeeded the following season by Blair.
The 2017 season was marked by the allocation of six points to some games to signify they counted as two fixtures in one.
It was a move that did not go down well with everyone, and it was no great surprise when Thistle voluntarily dropped to the relative stability of the Hawke's Bay-based Pacific Premiership.
But the road to New Zealand football's upper echelons takes in the Federation League and, with the competition set to comprise 10 teams, its structure looks more secure than it did three years ago.