AutoCAD - Why a step of DGN underlay deletion required before importing DGN ?

[timelapse1029]

Hi all, I hope all is well with you !

I'm learning about DGN import. 

According to the lecture video and practice exercise as well, there is a step of attaching DGN through X-ref, delete the underlay model, and then import the same DGN file via Insert tap -> DGN Import.

I tried just importing DGN without X-refing and deleting the underlay.

The end result is the same ! Is that right ?

Apparently it looks the same to me, and especially, the X-ref palette states that attached DGN is unreferenced.

How can I correct this unreferenced error if it is always an absolution to X-refing DGN as attachment and importing it ?

[ The subject line of this post has been edited to include the product name by @handjonathan ]

[TheCADnoob]

Without knowing the material you are referencing I'm not certain i can help.