Indemnities are extremely common, cheap (typically about £50), and effective. I've used them in just about all house sales, because someone forgot to apply for planning permission, or didn't have the right building regulations certificate, etc, etc.
Quite often, lack of paperwork will be made a non-issue by the passage of time (e.g. having no planning permission AND no enforcement by the local authority for 4 or 10 years, depending on the structure type, means it is lawful and cannot be pulled down.) But an indemnity, due to its very low price, is often offered anyway.
Offering an indemnity is almost universally accepted by the buying party as a means of covering the costs of any potential enforcement action arising as a result of not having the right paperwork for planning and all those issues. In fact, the clever owner will realise that buying an indemnity for the purchaser is at least ten times cheaper than getting the right certificates in the first place! More than once, I've considered indemnities the best-kept value for money secret going.
The indemnity offered by the seller to you now will cover you. It may cover successors in title, but I would expect in practice that new policies will be purchased each time the property changes hands.
Obviously, if 20 years have gone by since that planning permission, for example, was not secured and yet no enforcement has taken place, you can assess that there is no point offering as a seller - or no point seeking as a buyer - an indemnity for things that now will not happen.
In short, provided there are indemnities in place for you for each item of concern, and that your solicitor keeps and gives you copies of the policies provided, you should not consider this in any way abnormal, but what you ought to expect.