Problem creating & importing combined VCF file

[krappenessen]

I have been using MyPhoneExplorer on my Windows PC for some time, creating and updating my contacts as required. As I use a number of Android devices I decided to generate a combined .VCF file of all my contacts and import that into my Android devices. I create the merged VCF on my Windows 11 PC using:
Open "CMD"
Go to folder where individual VCF files are, eg "cd c:\contacts" Enter
Then, type in "copy *.vcf allcontacts.vcf" Enter.
I then copied the new combined.VCF file onto each of my Android devices and in the Contacts app I selected the
Import from file and in the past this worked fine entering the full data into my mobile.
However, because I have added and updated a number of contacts, today I repeated the generation of a combined .VCF file using the same CMD as before. Unfortunately this time for each of my Android devices when I provide it the new combined VCF file it gives the message:
"Couldn't import vCard"
So I have no idea as to what's wrong with my new combined VCF file when previously generated a combined VCF file by similar means it worked without any problem. I note I can still import each updated individual contact VCF file into the Contacts app
Another issue has now resulted in that on my Windows PC all contact records which were previously updated have been lost. Since as noted above, I can update these contacts on my mobile devices from the individual VCF file, is there some way I can import these individual VCF file onto my Windows MyphoneExplorer so as to restore it with the updates?

[icke1954]

To sync multiple Android devices use the setting F2 => Sync => Contacts => Sync with => Internal Sync-Database

[krappenessen]

To sync multiple Android devices use the setting F2 => Sync => Contacts => Sync with => Internal Sync-Database

Thanks for your response. Maybe you've misunderstood an important part of my problem:
I generate the master database for my contacts using MyPhoneExplorer on my Windows 11 PC. This database contains several hundred contacts and each such contact detail is held on a single .VCF file on my PC. I do all contact updates only on my PC (not on my Android devices) and then pass this data onto my Androids by importing the data via .VCF. Because I have so many VCF files (1 per contact), I have in the past merged all the individual VCF files together into one (using the method described in my OP). I've then copied the merged .VCF file onto an Android device and imported it into the appropriate Contacts app without any problem.
However yesterday my merged .VCF file was rejected saying "Couldn't import vCard". Why does this no longer seem to work? While I can certainly still import each individual .VCF file, this is impractical due to the number so that's why I merge them into one .VCF.

One thing I didn't mention in my OP was that I have just upgraded MyPhoneExplorer from v1.9.0 to v2.0. Could this effect my problem?

[icke1954]

Maybe you've misunderstood an important part of my problem:

That's right, I didn't understand why you have to make it complicated when there's an easier way?
I'll explain my suggestion again in more detail:
1. You need a separate user in MyPhoneExplorer for each Android device.
2. You activate for all users under MPE => F2 => Sync => Sync with => Internal Sync-Database
3. You change a contact in MyPhoneExplorer or create a new contact
4. By means of synchronization with the 1st Android device, the contacts are written into the sync database at the same time
5. Now you have to realize a sync with the remaining Android devices

If, for whatever reason, you want to keep your old method, I advise you the following:
MyPhoneExplorer => Contacts => Right-click on the contact list => Export/ Import => Export entire phone book

One thing I didn't mention in my OP was that I have just upgraded MyPhoneExplorer from v1.9.0 to v2.0. Could this effect my problem?

I don't think so, but you can simply install version 1.9 over it again.