Lily,
The OP - on her original post - WAS commenting on how spelling is taught:
"I was gobsmacked at the number of spelling mistakes which had been missed"
"the same mistake was made often without being corrected, for example Febury for February."
As I and others have pointed out, such spelling mistakes may not have been MARKED, but that doesn't mean that the teacher didn't notice them - there are good pedagogical reasons why a teacher may not mark every spelling error in a piece of work. However, for repeated errors as described, I would note the error in my planning, and plan it into my spelling lessons (which are separate from my main English lessons).
"Whilst others had been marked in green pen"
I use green, as is my school's policy, to show areas for improvement. Other schools use green to show that something is correct. The presence of green pen could mean either right or wrong.
"There were also some grammar corrections to things DD had written correctly."
If that is systematic (rather than a genuine error on the teacher's part - all of us are human, some of us mark until very late at night, and mistakes do happen.) then this is worth raising.
I would expect a teacher with poor spelling and grammar to be picked up by the leadership team in the school, and appropriate CPD to be put in place. I did work with a colleague who, despite being a truly excellent Reception teacher (used by the county to train others), found formal written English tricky. She was given specific support and continued training, and arrangements were put in place for proof-reading formal documents that she needed to send out in the interim - exactly as my relative weakness in PE teaching has been addressed through training, co-teaching and mentoring by a PE specialist.
For this reason, feedback to the school leadership about specific examples of poor English in letters and reports, if done appropriately, is very useful. However, it MUST go beyond a single example in marking a child's book that could be put down to a simple mistake.