It's not working for a very small reason. See, you set it to store his strength when he CASTS the spell, so any strength gained after he casts is lost in the end. that requires a small fix. Still, if you want to get a more efficient and accurate display of his power gain, i'd suggest modifying your damage trigger a bit. You only set it to detect when this guy attacks a unit, you can constanbtly click attack on random units and increase his strength without damaging units because your trigger doesn't detect if he hits or not. If you like it like that, that's fine. If not, you can check out my latest spell map for a damage detection system that'll clear that right up. That way, it'll only increase his strength when he makes contact, factoriung in misses as well.
As for your simple problem problem, there's 2 solutions you can choose from:
1: you can detect when he levels, and add that strength bonus to the initial amount. You'd have to add to it too whenever he uses permanent str boost items. At that rate, you wouldn't have to change your spell at all. but before you try that, read option 2.
2. Here's an easier way that takes care of everything: Instead of worrying about his intial strength, monitor the CHANGE in strength instead, then subtract it after. That way, you don't have to worry about leveling, items, or anything of that sort, just the damage he gains. This proves a lot more efficient and would solve your problem.
But the choice is yours. Do whichever you prefer. But notice that it's always easier to tackle the object of focus than to look at everything around it. Everything around is always monitored by the wc3 engine, you just have to focus on what you change. Hope this helps, and if you have any questions, should you choose to add the damage detection system, feel free to e-mail me, or pm me.