Doubtless Thistle will welcome their neighbours' embrace at Parkhead this afternoon without feeling the urge to ask "what took you so long"?
For most of the clubs' histories, Celtic have barely given Thistle a second thought around January 1, one of the plum dates on any league calendar. They last time they played each other close to the turn of a year was on December 27, 1969, when a Celtic team which would soon contest a European Cup final smashed Thistle 8-1. In 1912 and 1913, the clubs met on January 4 and January 3 respectively. Otherwise there is no history of the pair, whose grounds are four-and-a-half miles apart, meeting around New Year in those seasons Thistle have joined ever-present Celtic in the top flight.
A Glasgow derby is exactly what it is today - there is no doubt about that - but Thistle also know they will be summarily displaced if Rangers make their expected return to the top flight and are available for a New Year derby in January, 2016. In Glasgow, the phrase "Ne'erday Derby" means only one fixture. Thistle must be happy in their role as stand-ins.
When they were Old Firm games, the outcome of the December/January derby was often loaded with more significance than the others and could alter the mood and shape of what was nearly always a title race involving both teams. Tickets were like gold dust. For today's visit of Thistle, there has been a promotion allowing Celtic season-ticket holders to apply for two free tickets. Many fans welcomed that and some took up the offer, but it also has been an attempt to drum up interest in an unexciting fixture and do something to avoid the game unfolding against a backdrop of thousands of empty seats.
The game does not capture the imagination because it is so difficult to envisage Thistle being able to live with Celtic. With no threat to them being crowned as champions again, the most interesting aspect of the leaders' league fixtures at the moment is whether or not they can maintain their unbeaten record and emulate the achievement of 1897/98 when the club became champions without defeat (in what was only an 18-game campaign compared to the current one lasting 38).
"It's going to be tough because everyone is going to want to end the run when they play us, and they'll want to step it up another 10%," said defender Adam Matthews. "I think it would be a massive achievement [if they could go the whole league season without loss]. Everyone who plays us steps up their game so we have to be on our game every week.
"I don't know if you think about it at the start of the season. At that point you just want to get a good start and kick on. But once you win more games and keep on going you want to win as many as possible. Our aim is to go the full season unbeaten. It's going to be tough, but I think we can do it. Now and again the players talk about it among ourselves.
"Thistle have shown they can play nice football this season and we know every game from now on is going to be a tough one. When we played them away they gave us a tough game [Celtic won 2-1 at Firhill in October]. So we know what lies ahead and what to expect."
January 1 brings more than derbies. The transfer window has opened and players entering the final six months of their contracts are free to discuss possible moves with interested clubs. Both Georgios Samaras, linked with Hull City yesterday, and Joe Ledley have so far declined to accept the terms Celtic offered them to stay. "Joe has been a brilliant player since he came to Celtic," said Matthews of his fellow Welsh internationalist. "He is a mate of mine as well so hopefully he will put pen to paper on a new contract.
"It wouldn't be a surprise at all if there were clubs down south having a look at him because he has been a great player. I think a club like Celtic needs to keep all of our top players and Joe is definitely one of them."
Celtic will make January additions regardless of whether or not anyone leaves. Holmbert Fridjonsson, signed from Icelandic club Fram Reykjavik in November, is eligible to play from this afternoon, although he lacks match fitness. Among the names Celtic have been repeatedly linked with is Aaron Taylor-Sinclair, the Thistle defender. Left-back is an area Celtic want to address, but manager Neil Lennon said of the young Thistle man: "It's nothing to do with me, I don't know where the speculation has come from."
Lennon highlighted another sequence he would like to continue in addition to the unbeaten league run. "If we keep a clean sheet in the next game that's seven [over consecutive domestic games]. That's almost a club record. So the players have plenty incentive at the minute."