Visible in Viewport, not in modelspace

I received a drawing this morning, and it's paperspace looks great. However when I tried to view the drawings in modelspace it was empty. All the layers are on, when I click into the viewport (in paperspace) I can draw a line on the same layer as the block and that will show up in modelspace, yet no block.

Is this a feature of CAD, never experienced this before.

P.s. The blocks are available to insert in modelspace , however I'm just curious as to why I can not see the blocks that quite clearly exist in modelspace already.

If you can see them in paper space but not in model space, is it possible that these blocks were inserted in paper space?

Well they're visible on paperspace inside of a viewport. I am able to select the blocks after entering into the viewport and the space tab switches to model.

When you were in model space did you do a Zoom > Extents?

Yes, I did this initially and after I drew a line over the block in modelspace via the viewport. Extents managed to find the line, yet no block.

Let's back up. In one place you say "block" and in another "blocks". Is it one or more than one? What is inside the block(s)? What type of layer is the block on? What type of layer is the viewport on? Did you try to re-create the viewport? Are you in the World UCS or some other UCS? Which UCS is the viewport using? Are there objects in model space that don't belong to the block(s)?

In PS, make the viewport current, use View, save to a new name, go out to MS, use View, make that view name current.

Well there are three sheets, each sheet's contents (in modelspace) are a block. For example sheet P-170 has a block within it's viewport called P-170 and the entirety of the sheet is contained in that one block. Inside the blocks seem to just be lines on a layer which is on.

I was attempting to clear out all relevant info on the project so I could post the file, when I discovered the viewports aren't visible. Yet when I click within the linework I enter modelspace.

The file was too large to upload via this website so I went through yousendit:

https://www.yousendit.com/download/cnJoSlI1Qk45RlkwTVE9PQ

If you've got some spare time I'd appreciate if you guys could take a look.

Many thanks

Not sure why nothing shows in MS, but we are not dealing with core AutoCAD objects here.

Command: [b]dblist[/b]

Autodesk Inventor Object
Autodesk Inventor Object
Autodesk Inventor Object
Autodesk Inventor Object
Autodesk Inventor Object

                 VIEWPORT  Layer: "0"
                           Space: Paper space
                          Layout: P-100  COVER SHEET
                           Invisible
                           Visual Style: 2D Wireframe
                  Handle = fb
                           Status: On and Active
                           Scale relative to Paper space:    0.0268xp
                           Annotation Scale: 1'-0" = 1'-0"
                           View lock is on
           center point, X=1'-4 13/16"  Y=0'-10 1/2"  Z=-34'-9 1/8"
            width 2'-3 13/16"
           height 1'-5 7/8"

Well I'm just going to assume something was lost in translation between Inventor and CAD.

Thanks all ^^