Спасибо, как раз хотел у вас просить был ли подобный опыт. Вот что мне ответил агент на мой впрос по суммирование лет:
Hello Ilya,
If there is no gap in between legal stays in Poland and directly after that in NL then you must count from starting date in Poland (starting date mentioned on the Polish Blue Card) + 60 months, if the dates you mention below are correct then the 60 months end on 29-03-2023. After that date you can apply for a EU long term residence permit but keep in mind that during the processing time of that EU long term permit you must still have valid residency in NL.
Having said this, do you want me to apply for NL permit as Highly Skilled Migrant?