About innodb-auto-increment-handling

[five small]

Recently I learned AUTO-INC Locks, I see this DOCUMENTATION(https://dev.mysql.com/doc/refman/8.0/en/innodb-auto-increment-handling.html)
consider the following “mixed-mode insert” statement:(innodb_autoinc_lock_mode = 2)

mysql> INSERT INTO t1 (c1,c2) VALUES (1,'a'), (NULL,'b'), (5,'c'), (NULL,'d');

With innodb_autoinc_lock_mode set to 2 (“interleaved”), the four new rows are:

mysql> SELECT c1, c2 FROM t1 ORDER BY c2;
+-----+------+
| c1 | c2 |
+-----+------+
| 1 | a |
| x | b |
| 5 | c |
| y | d |
+-----+------+

In my opinion,there are only two cases :

y = 6
or
y = x+1

Am I right? Thank you.

Looking forward to your reply~