I'm a bit puzzled as to the best way to achieve the following:

I have rows which represent documents and they include an "Issued"
date column and a "Cancelled" date column. A document can have 3 states:
"Draft" (both date columns are null).
"Issued" ("Issued" date column is not null."Cancelled" date column is
null).
"Cancelled" ("Cancelled" column is not null).

Depending on the document state, other columns may be "locked" and
updates to them are prohibited. At all times some of the columns must
remain editable.

What is the best way to cater for the situation where 2 users open the
same draft document simultaneously and one user changes its state to
"issued"? This supposedly locks certain columns but the other user
still sees the document as a "draft" and can still update the "locked"
columns?

I'd be really grateful for any guidance on this.
Many Thanks
Mitch