You don't have to defeat two Bibarel to "make it count". If you defeat three Bibarel, you'll have 6 Effort Points in Attack; failing to defeat a fourth Bibarel won't cause you to slide back to 4. It's just that Effort Points don't translate into stat gains except in multiples of 4. You can accumulate Effort any way you wish; defeating 12 Machop, defeating 6 Machoke, defeating 3 Machamp, or defeating a Machamp, 3 Machoke and 3 Machop will all give you exactly the same result as far as building your Effort Values is concerned.

One other thing; the reason you have to wait until L100 to get 1 stat point per 4 EP is because collecting 4 EP grants you (your current level / 100) stat points. So if you're level 25 and have an Attack EV of 64, those 64 EP will raise your Attack by 4 points. At level 50, those same 64 EP will instead raise your Attack by 8 points, and at level 100 they'll be adding their maximum value of 16 points.