My contacts are not correct. Those who have two phone #s, only one transfers. Cant find a backup that is recent. Sorted my contacts and didn't like the result. You can last name, first name or the reverse. What a mess...fyi
I used Smart Switch to port my mom's contacts from her S6 Edge to her new S10. It worked really well. Can't remember if we had any issues with multiple 'same' contacts, however.
I know I have to keep some numbers together, and it'd be a pain if only one ported but not the rest!
I had a similar issue to that with some contacts as well. I noticed when I opened the contact and hit "edit" that some of those contacts had multiple sources across the top such as Samsung Account, Google Account, SIM.
Some had incomplete information, but I was generally able to find one that did have all the necessary info in one of the accounts.
I deleted the incomplete ones and then move the complete one if it wasn't already located where I wanted it.