My company has developed a system for schools to store information on
pupils e.g. grades, address etc. My job is to simply keep a log of
each school and record what stage of the integration they are at e.g.
some schools are now up and running with the new system, some are
having demonstrations etc.

I have just one input screen that allows you to select the current
stage for the school and enter the date at which they began the
stage. If they then move onto the next stage, you select the new
stage from the dropdown box and change the date. On a seperate sheet,
all the dates are stored. I have used the following formula for cell
X2 at demo stage

=IF($B2="Demo",$C2,$X2)

B2 is where the current stage is entered, so for the demo column, if
demo is the current stage then enter the date next to it (in C2),
else copy yourself. This is so the dates of previous stages do not
return to zero.

This is a circular reference and i'm guessing that the computer
doesn't like this.

Is there any way i can get the date to update in the new column and
remain unchanged in the old column (showing past stages) in a better
way?