Analogue machines, with belts and pinch rollers that can wear, tend to be even worse, hence all the money spent on time code or it's predecessors.
Hey, tell me about it ! The number of times I've tried to get analog machines to remain in sync without any kind of timecode. It's never worked and all that's happened is that my blood pressure has quadrupled and I've known a rage that even Darth Vader would've been wise to evade !
I don't want to jinx you, Grimtraveller, but you're very, very lucky.
As Beck said, even digital devices can (and do) drift unless they are specifically synced together with distributed wordclock or something similar. Years ago I had occasion to try and do a recording using two different sound cards--one of them a Tascam--and, even on takes as short as 3 minutes there was significant drift.
I'm amazed at that, to be honest. Would that apply to standalones too ? My DAW is
the Akai DPS 12i and it came out around 2000. I have 2, both bought 2nd hand, one in 2005 at a used instrument store in Lewisham, South London {via ebay}, the other last year in Hammersmith, West London, at one of the few remaining instrument exchanges that I know of. I initially bought the second one as a back up unit but I've been using it as regularly as the 'main' unit. I always have loads of projects on the go, I can't even say which is my main unit.
Sometimes, I record tracks from one project to another and I don't get drift. I'll often look at the numbers flying by and they're bang on, give a milisecond or so. It's been great for mixing because I use one as the mixdown deck and it enables me to mix in sections.
I thought that digital units always run at exactly the same speed and timing although in thinking about it, I have two digital clocks in my van, one on the stereo, one on the dashboard. When the clocks go back or forward I set them simultaneously and over a period of 6 or so weeks, they do drift apart. If I let it, it'll go as far as two minutes apart.
So...enjoy your system in the knowledge that you're very lucky. In fact, I suggest you go buy a lottery ticket !