Thanks to you all. I discovered the expiration of my KTN via TSA-Pre is still two years away. But we have two international trips coming up in November 2018 and March 2019. So I was thinking of purchasing Global Entry this summer so I'll have it in hand for my upcoming foreign trips. I would then change my online reservations/profiles to use the new KTN from the new GE.
We have credit cards that reimburse us for GE purchase, so I'm not too concerned about cost. I was more concerned about having two separate KTNs, but you've all helped alleviate that concern as it seems fairly common.