A quick scan of "The Definitive 1969 Camaro Z/28-SS396 Fact Book" published by Jerry MacNeish shows the following:
Page 11: 302 Engine. No clip
Page 13: 302 Engine. Both photos show clips (probably the same engine)
Page 17: "A Clamp mounted on this bracket on early production Z/28s to contain the heater hoses. Later production cars use a Ty-rap tin place of the clip"
Page 91: 350 Engine. Clip
Page 91: 302 Engine. Clip
Page 120: 302 Engine. In conclusive. Nov '68 built
Page 125: 396-375: Clip
Page 125: 427: Clip
Page 131: 396: Clip
Page 159: ? Clip
Page 163: 427: Clip
Page 181: Clip
And a quick scan of John Hooper's book, "The 1969 Camaro Reference Book", it shows 307s, 350 Pace Car, 396 Pace Car, 302's, ZL1's, 396/L89, 427's, Original Yenko Engine compartment, all with the clip...
Net-net - appears at some point there was a change in production from Clip to Ty-rap, Per Jerry's book, but when? My Van Nuy's April built car has the clip and had the original factory installed heater hoses, so while things can happen, would seem weird someone along the way decided to add that factory clip....so the change probably happened after April.