The CRG db has just over 1400 Z/28s; 18.55% are also RS.
I have seen many in my 40 years in the hobby. Owned one '83-'89; not only a virtual twin to the one just found in Brooklyn they are within 50 VINs. There were several more in the area. I have paperwork from Martz Chev; 3 of the 10 Z/28s they had were RS as shown in JM's '69 book. There's a Cortez Silver Z/28-RS featured in the book also. Friends also had them; Daytona Yellow/black vinyl/yellow houndstooth JL8 Z/28-RS and a 16k mile Le Mans Blue Z/28-RS that was recently sold. I have a small accumulation of factory paperwork copies; 7 more Z/28-RS including the Ron Pratte car sold at B-J AZ this year and another with JL8. Check out the April '69 Hi-Performance Cars magazine for a test of a Daytona Yellow Z/28-RS from Baldwin Chevrolet.
Nothing rare at all about a '69 Z/28-RS.