I had similar start to my career. Started as a sparks then moved into the alarm side for a company that only did alarms (within the security industry anyway)
I think the biggest thing IMHO would be to show confidence when talking about your work. Don't pretend like you know everything. You won't. But be confident in what you do know. I have only installed about 10 different panels in the last 15 years but have worked on dozens and I honestly think that because I know the terminology and the 'language' of the industry, things like FSL, EOL, ATS ratings, etc etc. (again not everything but feel like I know enough) that you could put me in front of any intruder panel with a manual and I would be able to get it up and running. Its just about knowing where the menus are for what you allready know you need to program.
Of course anyone can blag it as such in an interview but to be honest I think the manufacturers training only goes so far anyway. Experience (again only in my opinion) counts for way more.
I would say have a good think about the last year and the installs you have done. Are you happy with how they have been done? Have you had any callbacks on them that you can put down to your work? I would say if you are proud and confident in the work you have done over say the last year then thats a pretty good indicator to yourself of your abilities.