An IF function conundrum

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On my subscriber spread sheet I want to put an expiry issue next to their name in their contact details sheet. So I have three sheets I need to link data to. Here's an example of each:

Standard Subscriptions:
A B

Person 1	Issue 11 - August 2012
Person 2	Issue 12 - Febuary 2013

<colgroup><col><col></colgroup><tbody>
</tbody>

This

Data sheet:

G

Issue 01 - February 2010

Issue 02 - May 2010

Issue 03 - August 2010

Issue 04 - November 2010

Issue 05 - February 2011

Issue 06 - May 2011

Issue 07 - August 2011

Issue 08 - November 2011

Issue 09 - February 2012

Issue 10 - May 2012

Issue 11 - August 2012

<colgroup><col></colgroup><tbody>
</tbody>

and so on

I use this to create a drop down list for column B in standard subscriptions.

Now I have another sheet which holds all their details called contact:

Name Company Address Email Expiring Issue

Person 1	Success company 1	Flashy Address,	Email@person1company.com	Help Here
Person 2	Successful company 2	Another flashy address	Email@person2company.com	And here

<colgroup><col><col><col><col span="2"></colgroup><tbody>
</tbody>

What I would like to do is create an equation that will automatically place the expiring issue into that column. The expiring issue is always 4 cells below from the data sheet. So if they subscribed on issue 1, the last issue will be issue 4. Something that's proving a little bit of bother is that some details appear more than once in the subscription sheet as when they renew they are placed on the sheet again so it would have to be connected to their most recent subscription.

I've tried playing around with IF and vlookup formulas but I can't seem to get it right. Is this even possible?

Thanks!

 

[SuchHelp_MuchThanks]

Bump. No takers?

I would really appreciate the help!