Possibly selling primary house this year. Is there any reason in the following circumstance to have an accurate basis?

Inherited 50% of house a couple decades ago, and inherited the other half interest about 15 years ago.  This is primary home.   So have owned the whole house for 15 years.  I know the appraised value for the first half, but an appraisal was not done for the second half, since it was not needed for the small estate with sole heir--just a title transfer.

As an example, the first half interest had a basis of about $40K and the second half interest would have likely had a basis of say $50K or so if an appraisal had been done at the time.   Current value of whole house is about $110K.  That would be a gain of about $20K if using fully-appraised basis from the 2 prior events.

I realize I could pay $200-300 to have it appraised retroactively, but since the gain would only be approx. $20K when fully appraised, is there any reason to do so?   Even if I only used the first half value of $40K and ignored the second half basis, the gain would be $70K.

Since this is preliminary at the moment, I don't know if I will get a 1099-S or not.  I'm hoping I can talk them into not submitting one.  I don't think they have to give submit one for a primary home with these value amounts, do they?

In summary, is there any need to pay for a back appraisal?  Am I likely to get a 1099-S?

Thanks.