[smartalexx]

Partner led a 4th best at NT and You played an Honor to that first trick .
shortly after you are in hand and play back partner's suit.
Usually you should play current count of the remainder....but this is true only 90% of the time. main exceptions types are:
either for unblock reasons
either for overkill reasons(partner will have difficulties to believe you have 9 or 10 cards together in the led suit

could anyone document with real life examples or theory?

[HardVector]

smartalexx, on 2019-April-24, 00:41, said:

Partner led a 4th best at NT and You played an Honor to that first trick .
shortly after you are in hand and play back partner's suit.
Usually you should play current count of the remainder....but this is true only 90% of the time. main exceptions types are:
either for unblock reasons
either for overkill reasons(partner will have difficulties to believe you have 9 or 10 cards together in the led suit

could anyone document with real life examples or theory?

So, if you hold a singleton or doubleton, there is no problem is what to lead back. If you hold Hxx, then you should lead back the highest remaining card (showing a current doubleton). Normally, holding Hxxx, you should lead back the original 4th best, or low from the remaining xxx. You already mentioned the most probably reason, to unblock. Say you have KT92 in partner's lead suit. If declarer has AJ doubleton with a small doubleton in dummy, partner holds something like Q8xxx. If you lead back the 2, the suit blocks. So, this is a case you suspect partner holds 5 cards and you want to get out of the way. The other case, is you know (or suspect) that declarer has 4 cards in the suit and you will need to finesse twice to gain the tricks you are due. So, same scenario, you hold KT92 and partner leads the 3 with a singleton appearing in dummy. You want to play the T so you can finesse twice if necessary. If declarer started with AJ8x, then there is nothing you can to about it, declarer is getting 2 tricks from the suit. But if they started with AJ7x, then you get 3 tricks (assuming partner started with Qxxx). If partner lead 4th best from some holding like 8643, then that is a conversation you need to have with partner.

[Vampyr]

HardVector, on 2019-April-24, 19:12, said:

If partner lead 4th best from some holding like 8643, then that is a conversation you need to have with partner.

Hi. Your English is far better than my grasp of your native language and I can say that without even knowing what language that is. Anyway, it is lead, led, led.

The person to consult is Krzysztof Martens. In his books, particularly Guide Dog volumes 1 and 2, it is likely that he illustrates times when doing something else is more important than leading back a count card, and how both players will know why and what is being shown. This assumes that you are willing to do some hard work as a partnership.

[HardVector]

Vampyr, on 2019-April-24, 20:50, said:

Hi. Your English is far better than my grasp of your native language and I can say that without even knowing what language that is. Anyway, it is lead, led, led.

The person to consult is Krzysztof Martens. In his books, particularly Guide Dog volumes 1 and 2, it is likely that he illustrates times when doing something else is more important than leading back a count card, and how both players will know why and what is being shown. This assumes that you are willing to do some hard work as a partnership.

I've read some of Martens books, but the translation from Polish was unimpressive. I'm sure that in that language it was impressive and comprehensive, but translators don't get it right very often in my experience. I just gave some general examples of the most common times you would not give count. I think that the original posters assessment of 90% of the time you will give count may be accurate.