Update deck via extended .csv with new synonyms, avoiding old duplicates

Trying to debug the error I have just found, which I have mentioned in my previous comment, I have been playing around with a simple test deck, which starts empty:

#separator:tab
#html:false
#guid column:1
#tags column:1

I then extend the TXT:

#separator:tab
#html:false
#guid column:1
#tags column:1
\t key1 \t val1 \t
\t key2 \t val2 \t

I import that into Anki:

I export it again, its associated TXT now looks like this:

#separator:tab
#html:false
#guid column:1
#tags column:3
b_6Wi?(RWH	key1	val1	
B^!`PV?x<R	key2	val2	

Now, I extend the TXT with another key-value pair, this time, we are re-using an existing key:

#separator:tab
#html:false
#guid column:1
#tags column:3
b_6Wi?(RWH	key1	val1	
B^!`PV?x<R	key2	val2	
\t key1 \t val3 \t

I import it into Anki again:

And here comes the problem:

Anki does not detect that the new line, for which a GUID field was missing, is a new note: instead of assigning a new note to it, it uses key1 for comparing the notes; since key1 has already an existing note, it simply updates it

This is what the deck looks like when exporting it now:

#separator:tab
#html:false
#guid column:1
#tags column:3
b_6Wi?(RWH	key1	val3	
B^!`PV?x<R	key2	val2	

Thus, it seems like this guidance does not seem to work for the case of synonyms, @BookBorsh:

How can I make it work, so that I can manually extend the TXT file and import it into Anki, with Anki assigning a new GUID to it, also for the case of synonyms?