Getting Subsequent Records From Same Table

I was trying to use inline views, then sub-query etc. Still can't get quite what I want.

So for example take a personID where they are registered, processed and deregistered. They can have one or more registrations, one or more related processes (for each registration) and then deregistration, the processes are always tied to a registration and deregistration period.

for a given time-period I want to find the first registration and use that first registration to find subsequent registration records within 20 days - I don't want to return processes related to the next registration record, just the next registration record.

I already have the query built that returns all the raw data for those registrations, processes and deregistrations but need to set up something that finds subsequent registrations. So here is a sample of raw data:

Person Id RowID Reg_Date Reg_Time Process_First_Date Process_First_Time Process_last_Date Process_Last_Time De_Reg_Date De_Reg_Time
========= ======= ======== ======== ================== ================== ================= ================= =========== ===========
000000001 00001/8 01/01/2014 12:00 01/01/2014 12:00 02/01/2014 11:40 03/01/2014 16:44
000000001 00001/10 01/01/2014 12:00 02/01/2014 13:22 03/01/2014 09:56 03/01/2014 16:44

[Code] ....

firstly need to use all first registrations - that would be row where reg-date = process first date and also reg time and process first time are equal - and use those for finding the next reg_date of that personID. PersonID can have more than one registration in a period so need to do something like partition, which although it worked on it's own, seemed to become a tangled mess when I started using the subset in a inline view or sub-query. Not sure how to return earliest reg date in period for certain PersonID for multiple IDs.

So for above I would want to return these rows:

Person Id RowID Reg_Date Reg_Time Process_First_Date Process_First_Time Process_last_Date Process_Last_Time De_Reg_Date De_Reg_Time
========= ======= ======== ======== ================== ================== ================= ================= =========== ===========
000000001 00002/12 04/01/2014 10:36 04/01/2014 10:36 05/01/2014 15:12 08/01/2014 12:33
000000002 00004/13 04/01/2014 10:36 04/01/2014 10:36 05/01/2014 15:12 08/01/2014 12:33

And this is based on these two rows:

Person Id RowID Reg_Date Reg_Time Process_First_Date Process_First_Time Process_last_Date Process_Last_Time De_Reg_Date De_Reg_Time
========= ======= ======== ======== ================== ================== ================= ================= =========== ===========
000000001 00001/8 01/01/2014 12:00 01/01/2014 12:00 02/01/2014 11:40 03/01/2014 16:44
000000002 00003/9 01/01/2014 12:00 01/01/2014 12:00 02/01/2014 11:40 03/01/2014 16:44

I have made the dates the same in last 4 rows, this isn't intentional and doesn't mean anything it's because I copied and pasted the first 4 rows.

How to tie this together using first reg of each personID and then comparing with other records to find subsequent first registrations. I'm not too fussed about finding them within a certain time period from the first registration, more that I want to just get some sort of query set up then I can put in specifics.