In fact, I was thinking about 2 things :

1) Is it possible to block a flail ?

2) Have you ever seen a sai dealing damages and not disarming ?

IMO, these events can happen.
But I have never seen a flail being blocked by a shield.
I think I have already seen my sai dealing damage without disarming but I'm not sure and I don't have any fight to prove this.

Do you have these kinds of fights guys ? Or do you think it's not possible ?

Flail I'm 99% sure it can't be blocked, I have never seen it atleast (And I
have quite a few shield/counter and flail brutes), the sai's disarm isn't 100%
from what I know. I'll try to get a fight of it in somedays

I have had tons of experience with both of these scenarios and from what I've seen, the flail can never be blocked and the sai always disarms weapons. The sai however does not always disarm shields, although it does more often than not.

1)I don't got the fight but i see one , u just need another heavy weapon like etoile du matin or hache , and some luck XD

1) Don't know.
2) Always saw saï disarming on hit but well, I'm still kinda new on this game.

1) Is it possible to block a flail ?
well there is only one weapon which some say that it is the best blocking weapon in the game combined with counter and shield,
and because it is very rare to find a brute with this set, i say we could start searching for this brute and then we can answer this question.
but other than this Option, i have never seen a Flail getting blocked at all. and i had a very long journey with RicoRico and RicaRica fighting with the Flail as an only weapon set.

2) Have you ever seen a sai dealing damages and not disarming ?
well as mantis mentioned the shield will not allways get disarmed.

but as the matter of fact i have seen it a couple of times where the Opponent has a weapon and a shield in his hands and the sai disarmed only the shield but the weapon remained in the opponents hands.
but imo this is only a rare special case of your question and the general answer should be "no"