Employment gaps

I'm going to have to add alot more into my work history since 2003 as I went through a handful of short term jobs before I stumbled upon on this last ten years of relative stability. They're asking for dates which I would have to guess and not sure how many times I can put on my gaps in history as "left for another job".

Hi sorry, i have been a little unwell and therefore not online. personally, when describing the role i would add something at the end highlighting that it was a temporary role: For example: May 2003 - Administrative Assistant (Temp Cover) -> then where it says 'reason for leaving' you can put Temp Cover Role or something like that. At least that way you have said you went in to cover a role and why the term was short. in addition to this, I would leverage your ability to cover roles on short notice as being a strength i.e. I am a fast learner and enjoy learning on the job as highlighted by my employment history where I have filled in at short notice as temporary cover. This has allowed me to develop significant transferable skills which i can bring to this role including being able to build rapport with colleagues quickly, the ability to rapidly integrate myself into a team and the ability to work with wide cross-sections of society as well as excellent, adaptable communications skill. This is an exampley that you are free to use and adapt. apologies for the delay and i hope it is helpful

Hi,
I'm applying for an admin assistant job and on the application form it's asking me to list employment gaps since school(!).
I think I can just about remember my work history since school as most of it is taken up my education spells (college/university) so I assume I am writing all of this down in this section?
In addition, how far do I go back with my employment history? I've normally tended to go back 10 years on my CV but with the aforementioned question, I'm thinking do I need to list all jobs I've had, some of which that weren't for long.
Any pointers would be appreciated.
Thanks!