Does interlining of bags usually work pretty well? I flew a few weeks ago MSP-EWR on NW using one NW-issued ticket, and then later the same day EWR-BRU on 9W using a seperate 9W-issued ticket.

I thought about asking for the bags to be interlined but I was worried it would get screwed up and they would get lost. So I collected my bags at EWR and then carried them up to check-in for 9W.

I also worried that NW would do something to my MSP-EWR ticket since I thought the contract of carriage didn't allow you to purchase seperate tickets just to reduce the cost of an itinerary (I did the same thing in reverse on the inbound from Brussels).