It depends on their state rules, and normally they are not considered as regular sale deeds and may help for claiming possession and mutation in revenue records at the maximum during olden days. Some states enacted to collect such stamp fee and regularize such old sale deeds of more than 12 years old written on normal Rs.20 stamp paper. The agreement is different from actual sale. When it is not valid for the purposes of law, any one interested to make things complicate or claim a share may point out illegality and unenforceability of such sale. Possession and enjoyment with revenue records may strengthen the argument but it is not a normal legal title deed.
No, such documents are not valid for transfer of property. The document shall be registered and proper stamp duty be paid for its validity. Feel free to contact at email@example.com for further assistance.