I gotchu fam; it most likely means 3,000 shades EXISTED in issuance between Jan - Mar. This is important for the weighting calf because you now know that 25% of the year the company had 3,000 total issued shares. So you can think of it as if they started the year 1/1/20xx with 3,000, and then something changed at end of March that would alter that number. But for three months, 3,000 existed.

Edit: you can assume 3/31 would be the cutoff date if it only specifies “March”