Thanks, guys. Especially H. for the link to the current comp rules. The set of rules I linked to was from WOTC, but a year plus old.
Cutlex says "Convoke and Delve are specifically written as exceptions to Trinisphere." Huh? The word "specifically", I guess, could have either the meaning that the definitions of Convoke and Delve actually reference Trinisphere by name, which they manifestly do not, or possibly that the writers had Trinisphere in mind when they wrote those definitions. I'm not sure how we would know the latter.
Also thanks to ChubbyRain for the further explanations. The Dig Through Time reminder text, though, just goes to illustrate why I continue to feel uneasy. That says, "(Each card you exile from your graveyard while casting this spell pays for 1.)" (Aside: How do you do blockquotes on this forum software? ) But the CR says:"you may exile a card from your graveyard rather than pay that mana.”
I know I'm just quibbling now. I agree we've established the correct answer to the interaction of Delve and Convoke with Trinisphere, but in a game where the comprehensive rules run to a couple of hundred pages, you'd think they would try to get their wording consistent. I guess I'm just feeling grumpy. I'll try to behave.
Anyway, thanks to everyone for your efforts to educate me.