This flaw is very inconvenient. There needs to be a Settings switch for contact numbers so category can be changed from Notices to Personal, and vice versa.
I did find that when Google Android changed over to using “+ country code” before every number, that if I added that country code + number as a new phone number in Google Contacts that this new sms line went in to Personal but left behind all the previous msgs in Notices. Very inconvenient.
Please build a solution into an update.