If the hazards, risks and control measures haven't changed as a result of the transfer, then there's no pressing need to change the content of the risk assessments when the headings are changed. 

However they will need to be reviewed at some poiut (there should be a set period for reviewing them - this may be mentioned either on the risk assessments or in company policy).   They will also need to be reviewed if there have been significant changes or if new issues are identified (for example, if there is an incident that leads to questioning of the risk assessments).

If the reissue with changed headings wasn't accompanied by an actual review of the content, then it would be dubious to use the reissue date as the starting point for measuring the time to the next review.

If every RA needed revisiting the instance a post holder changed you can bet business would have thrown this up in the Red Tape challenge several years back.

It is more normal practice during a take over to conduct "Due Dilligence" - in terms of H&S arrangements what is currently available should have been considered and where suitable will be left alone until the next review period. Gaps between existing and required (by the new operator) will have been identified on a priority list for action.

The RA is a company document and does not require the permanent presence of the original author. By copyimg the existing document to their letter head the new company has demonstrated its belief in the RA content and taken direct ownership.

The only document I would expect to see revised solely due to a change in post holder would be the signatire at the bottom of the company QHSE policies to demonstrate the commitment of the person at the top.

I agree with Roundtuit.  When I start in a new company and find that my predecessor who has now left has signed off all the risk assessments, I regard them as still valid until there is reason to think otherwise. 

The authoring and sign-off of risk assessments is done by individuals on behalf of the employer, and so their validity isn't affected by those individuals leaving.  The employer still has ownership of them.