Excel 2007 : Calculate Days Since Last Stage, where some stages don't occur

Hi Guys, first post here,

I've trawled a few forums with this issue, but admittedly I could have looked a little harder, so apologies if this is easily answered on another thread.

I'm monitoring a set of projects and want to report on the number of days taken since the last step, which is are set out in a numeric order (i.e. step 1, 2, 3 etc). However not every project needs to go through every step (i.e. 1, 2, 7, 18 etc).

I have a table with rows as a record of each event with other projects mixed in together, i.e.

Row 1 - Project A - Step 3 - 04/11/10
Row 2 - Project A - Step 4 - 05/11/10
Row 3 - Project B - Step 3 - 06/11/10 etc

I have a pivot combining all this data and apart from setting up a set of nested IFs (I have 39 steps in total so a nested 39 IF formula doesn't appeal) counting back each step until in finds a cell with a date, I can't think what else to do.

I want to be able to say, "this project took X days to go to Step 7, then X days to get to Step 8, this project didn't do Step 9, but it took X days to get to Step 10 (from Step 8)".

It also needs to accommodate that some events might occur on the same day and therefore be 0 days between the last step.

I'm running 2007 and have a basic understanding of VBA, though I would prefer not to use it as the file is going around several Government departments where IT security is pretty tight.

I hope that's clear.

Will sincerely appreciate any advice you can offer.

Ali