How comes SCN difference between "expdp dumpfile" and "impdp result" around instantiation SCN?

Hello, Oracle experts.

When using 19cDB, I want to know around the difference of SCN derived from a dumpfile made by "expdp" command, between:

1. extracted from the dumpfile by "impdp" with sqlfile option

2. registered into the "DBA_APPLY_INSTANTIATED_OBJECTS" table while importing by "impdp" command

I checked this twice, SCN of "1." is slightly earlier than SCN of "2.".

(For example, around "1.": "sys.dbms_logrep_imp.instantiate(...,inst_scn=>'68015855',...);", and around "2.": "SQL> select INSTANTIATION_SCN from DBA_APPLY_INSTANTIATED_OBJECTS where SOURCE_OBJECT_OWNER='...'"->"68016225".)

If you know the reason, please let me know!!

Thanks in advance.