A muʿanʿan isnad uses “ʿan fulan” (“from so-and-so”). It is not the same as the explicit audition formula “I heard so-and-so.” Hence documented contact and possible tadlis matter when evaluating a chain.
Hypothetical example: “Zayd ʿan ʿAmr ʿan Khalid.” If Zayd and ʿAmr are known to have lived at the same time but no meeting is documented, the assessment may vary with the adopted criterion. If it is proved they never could have met, the word “ʿan” does not repair the break.
Conclusion: “ʿan” is neither automatically accepted in every setting nor automatically rejected in every setting. Narrator circumstances and chain evidence determine its significance.