Hoping this is a good board for the question.
Intonation, with guitars it can be caused by old strings. I realise there are many other things that could be the cause, but, for now i am only curious to learn if sticks have this issue, and if so, how often the strings should generally be changed, to avoid it?
Followup to the above, does SE get strings to us rapidly enough when we order them? I would Hate to go 12-14 months between practices because of a string issue! Or would it be good, or possible, to use strings made for another instrument?

To remove stress in your life, why not have a spare set of strings in your gig bag? If one or two strings aren't behaving properly, swap em out. You can always order individual strings to make your spare set whole again.

I use a lot of pitch bending and sliding when I play. Stretching the strings to the extremes most likely is not helping with intonation. Sometimes, I get so wound up in the music that I don't notice that I'm out of tune. When I take the time to tune the instrument again, it sounds different. I prefer to play a bit out of tune at times, it's very organic and not sterile.

I'm my experience the answer is a clear yes.

Though I'm only a little over a year into my Stick adventure it's been with pre-owned Sticks and I've been experimenting with various tunings so I've placed several string orders. Each order has been despatched promptly by Jeff.

I'm in the UK, which obviously complicated delivery, but SE to me by UPS has typically been 10-16 days.

My last order (for a 'flat' belt hook mount) was in my hands in just under a week! Both I & Jeff were amazed. It was just after New Year and I think we must have hit a quiet time for the carriers or somesuch?

Excellent! Thank you both!