Querying sys_history_line tables

I have a requirement to query against the sys_history_line table and retrieve some information.

I had a request to display the "fulfilment" date on a Portal record.

On checking a couple of records, I can query the sys_history_set and then the sys_history_line

I soon realised this was not great for the portal so I have added a new field to the sc_request and sc_req_item tables.

However, now I am being asked to back populate the data

i have had a look at pulling from sys_audit and from the sys_history_line tables.

the later are better for my needs.

I am however finding that when I run a Background Script to get some data I am offten getting a lot of null information for the field I am after.

Script: REQ0015788 : b76ef6ec6f1782402a3e9accbb3ee4ac : 2015-10-21 10:03:36
*** Script: REQ0015776 : 43b86b0d6f6346007115ca727d3ee404 : 2015-11-04 12:40:15
*** Script: REQ0015763 : 6d2d55df6f5f4200b872129e5d3ee424 : 2015-10-29 16:01:48
*** Script: REQ0015756 : 22db3cd76f5f4200b872129e5d3ee43b : 2015-11-05 10:49:29
*** Script: REQ0015750 : d05479956f970200b872129e5d3ee47a : 2015-11-05 10:49:30
*** Script: REQ0015749 : 421179d16f970200b872129e5d3ee4c9 : 2015-11-05 10:49:32
*** Script: REQ0015744 : c2d7c15d6f570200b872129e5d3ee439 : 2015-10-29 16:24:22
*** Script: REQ0015737 : cc16a0496f930200b872129e5d3ee435 : null
*** Script: REQ0015605 : f35b82dc6f5f42402a3e9accbb3ee4eb : null
*** Script: REQ0015600 : 74f84a5c6f5f42402a3e9accbb3ee492 : null

If I now go into the record REQ0015744 and come straight back out and run the Backgroun Script again, I now see the information

*** Script: REQ0015788 : b76ef6ec6f1782402a3e9accbb3ee4ac : 2015-10-21 10:03:36
*** Script: REQ0015776 : 43b86b0d6f6346007115ca727d3ee404 : 2015-11-04 12:40:15
*** Script: REQ0015763 : 6d2d55df6f5f4200b872129e5d3ee424 : 2015-10-29 16:01:48
*** Script: REQ0015756 : 22db3cd76f5f4200b872129e5d3ee43b : 2015-11-05 10:49:29
*** Script: REQ0015750 : d05479956f970200b872129e5d3ee47a : 2015-11-05 10:49:30
*** Script: REQ0015749 : 421179d16f970200b872129e5d3ee4c9 : 2015-11-05 10:49:32
*** Script: REQ0015744 : c2d7c15d6f570200b872129e5d3ee439 : 2015-10-29 16:24:22
*** Script: REQ0015737 : cc16a0496f930200b872129e5d3ee435 : null
*** Script: REQ0015605 : f35b82dc6f5f42402a3e9accbb3ee4eb : null

arrgh Is there any way I can make this work - it will be a background task run once for the sc_request and sc_req_item tables

It is as if I need to open and inspect each record or somehow force the history tables to work

I did try a query against the sys_audit table and it was seemingly having a similar issue

any ideas would be gratefully received