Svend Madsen Solid Desk Top?  

How about some photos of the rest of the desk so that we know what model this is? That would sure make it easier to help. Snap a photo of the end grain glue joint while you are at it as well.

Hey Leif!
Its the same model as the 1stdibs link and found here on danish furniture index: https://aleph-01.kb.dk/F/2PAJMEP14DQ9UQ66HDY15PD5AH3FQQLDD9Y1PHPVLB2EC86...

How about a close up of the end grain glue joints?
Are there any really light areas in the wood (sapwood) on the underside of the top?

Yes they look like long strips of wood glued together.

What kind of wood is the top?

I was curious to see if the seams between the pieces of teak look original (and the glue).
The pieces of wood look like a lower grade than I would expect.

Agreed. Hence my concern. There are visible knots on the top and it appears to have a thin coat of poly.

A coat of polyurethane would not necessarily mean a lot (it could be later production, or refinishing). And I have seen the occasional 1/2" knot in era teak pieces.
Again a photo of one of the seams in between the boards in the top might reveal a lot. (There are difference in the way that it would have likely been done in a production environment in the 50s-60s vs as a custom replacement later).
Another thing to look at would be whether the top was attached to the frame in the proper fashion for a wood top (to allow wood movement). If you take photos, I would be happy to give you my thoughts.
If it has not been attached properly, it would suggest that it was done quite recently, in which case it hasn't seen much humidity variation, and/or the polyurethane is still slowing humidity migration enough to protect the top from much movement. (And you would want to remedy the situation before some bad thing happens like the top breaks the desk or itself, or bows, or a bit of all three).
It is possible that you might also notice that the mounting system has been modified to allow for a solid teak top, which would be good, but might also indicate that the factory did not plan for a solid top.
Or finally, you might discover that the mounting was done right by the factory, which would be a pretty solid confirmation that it was intended to have a solid top.

Leif,
Here are two photos from underneath. Thank you!!

I still don't seems they mounted the top to the desk, but I do see all sorts of patched flaws in the wood. And notice how much higher grade the rest of the wood is.
And somehow that does it for me: it is a replacement top.

Leif, I think that you nailed it (no pun intended). The top is most likely not original to the piece.

Thank you Leif. Thats what I expected. Appreciate your insight as always.

Leif- could you provide any info about this Madsen desk? I haven't found that design (legs) on any others on-line. Thanks!

Marnie - Can you provide detailed photos of the legs? How they mount, etc? Also, is it marked? Most Madsen desks have the burned in logo under the drawers.
Thanks.