Sounds like you did not match the data with the fields Thunderbird expects to see. Here is a pretty good tutorial. https://www.howtogeek.com/79968/import-gmail-contacts-into-thunderbird/

Thank you, but I must have done something right as 660 records imported correctly while only 30 were wrong. It seems that the wrong ones did not have either a full name or a full address in the csv file. Does that mean each of the 693 records has to be manually adjusted during the import process?

No you do it once for the entire import. I would say you those 30 records were not in the same order as the successful ones.

Examine your CSV file and confirm the same data is in the correct columns.

I have been over the whole csv file, (trimming it down to 470 records in the process,) and not found any errors. Reinstalling the address book still scrambles some of the records. Any further ideas?

No, it is a pretty straightforward process that has worked fine every time I use it.

Is it the same contacts that are not correct each time you import?

That's a blow. Without my contacts list Thunderbird will not work for me, and without email the change from Windows to Linux is no longer viable.

I have read elsewhere of extensions such as Tzpush which enable the import of address book, but the extension is incomprehensible to me. Are such extensions of any value?

I have never used or heard of them so I cannot advise.

If all but 30 import correctly what is wrong with just fixing the few with errors?

Yes I could correct those that are obviously wrong, but I would then doubt whether the other 440 records are right, and that is too many to manually check and correct.