If I do NOT know the date of burial, I will leave it blank.
I was raised in the mountains of Colorado, in the winter when some one died there was a funeral a few days later, but the burial may not have been until later in the spring.
The ground was just to hard to dig the hole. This was before the day of the backhoe and other machinery to move earth around.
Some areas today, still do not have burials in the the winter.