Bringing in Data from one Worksheet to another based on matching multiple fields

In a bind -

I have 2 spreadsheets basically the same information except one worksheet has an extra column. That extra column was completed manually 3 weeks ago. I need to pull that information into the other sheet that is to be pulled on Monday - HOWEVER - the 2 sheets will not be exactly the same. I am pulling from a database and some rows will drop, some have/will change values, so its not like the rows will match up anymore. I have done tests - trust me they will not. AND of course what I should have done is downloaded the email address which would have been the ID for that row, but it was not.

So what I really need to do is find the values for 3 specific fields (A1-Date, A2-First and A3-Last Name) in one row in Sheet #1 and if they match the 3 fields in the new sheet (SHeet #2), enter the value from the manual field (Rider #) in Sheet #1 into a new field in Sheet #2. But if they are not in the same row it will not work. I tried an -IF(And.. formula but that only works per row. SO how do I find the 3 matching fields in other rows? IS it possible?

We are only talking about 9000 records BUT it would take me all day probably to do the If(ANd and then finish the rest manually, because as you know once one row is out of sync they all are out of sync after that.

Also I basically need to do the same thing again on Thursday - compare sheets, if this info matches then compare total fields. Then do a change report. Look forward to hearing from anyone on how to do this.

I have seen VLookup mentioned but I don't think that will work across 3 fields, and if so I can not figure out how.
And I really don't have time to figure out Access.

At the office I am on a PC. Excel 2010 I think but will have to check tomorrow.

Added a template file with 2 tabs so you can see what I mean. Thanks!!! - Karen

1) In the OLD DATA sheet,

Y1: Key
Y2: =A2&"-"&B2&"-"&C2

Copoy Y2 down the Y column as far as needed.

2) In the NEW DATA sheet:

D2: INDEX('old data-with rider number'!D:D, MATCH(A2&"-"&B2&"-"&C2, 'old data-with rider number'!$Y:$Y, 0))
...copied down.

To resolve the #N/A errors, use:

D2: =IFERROR(INDEX('old data-with rider number'!D:D, MATCH(A2&"-"&B2&"-"&C2, 'old data-with rider number'!$Y:$Y, 0)), "none")

3) Copy column D, then do a Paste Special > Values to remove the formulas and leave the results behind, if needed.