i use jack's RO 12-4-16 from start to finish. i don't believe you need a veg nute, a transition nute, a bloom nute and a finish nute like many others. just like i don't think you need a PK booster.
They didn’t sell bloom boosters and all that snake oil when I got into growing and my yield/quality was great.
The line I ran for rockwool was Europonic and they did have different ratios for veg and flower. I attempted to mention, but never finished the thought really, that due to circumstances (going to grow store not trivial) I used the bloom (2 part-A&B) in veg. It worked so well I never bought the grow A&B after that.
So while I am still experimenting with the efficacy of increased P/K myself I think not using it may be some good advice. I’d recommend fulvic and kelp over P/K boosters.
But back to flushing. As I stated that too was never a thing a while back. I don’t go out of my to flush. About a week before harvest I don’t bother mixing up new nutes so if the reservoir is low I top it off w water. And if fir some reason I need or decide to chop a little early I don’t worry about if they were flushed or not.
Imagine going to the grow store and this was it for inorganic fertilizers to choose from lol.