Adding numbers from several worksheets with a common bond

[C Monehan]

I have a spreadsheet of employees and their 401(k) contributions. Each pay
period is set up on a separate worksheet within the spreadsheet.

The employees listed for each pay period are sometimes different (i.e., Jane
Doe may be on the first worksheet but not on the second, because she was off
work in the hospital).

I need to look at the list of employees which are set up with their last
name in one column and their first name in the second column.

If both the last name and the first name in a range of cells match the last
name and first name in a range of cells on another sheet, I need to add the
amount of their YTD deferral (separate column) to my current pay period
deferral and display it as the current YTD total.

Example:
Sheet 1
Last Name First Name Deferral YTD Deferral
Doe Jane 37.21
37.21
Doe John 53.00
53.00
Smith John 16.45
16.45
Smith Mary 11.15
11.15

Sheet 2
Last Name First Name Deferral YTD
Deferral
Doe Jane 1.00
38.21
Hall Jerry 98.44
98.44
Smith Mary 25.00
36.15

Can this be done withouth having to put the first and last name in the same
column?

I can use the SUMIF, to calculate it based solely on last name, but when
there are two people with the same last name, I can't split up the
information.

Any suggestions?