In the korech section of the hagadah there is an introductory paragraph. In most hagadot that I have seen, the phrasing says:
הָיָה כּוֹרֵךְ מַצָּה וּמָרוֹר וְאוֹכֵל בְּיַחַד, לְקַיֵּם מַה שֶּׁנֶּאֱמַר: עַל מַצּוֹת וּמְרורִים יֹאכְלֻהוּ.
He would wrap the matsa and marror and eat them together, in order to fulfill what is stated, (Exodus 12:15): "You should eat it upon matsot and marrorim."
However, in a number of Hagaddot, such as Passover Haggadah: The Feast of Freedom" The Rabbinical Assembly, 1982 and, I think Rav Riskin's Hagadah, IIRC, I have seen the phrasing:
הָיָה כּוֹרֵךְ פסח מַצָּה וּמָרוֹר וְאוֹכֵל בְּיַחַד
He would wrap the matsa and marror and Pesach sacrifice and eat them together
To me, it seems that the 2nd version is correct, assuming that Hillel was doing things correctly, as he was supposed to eat the Pesach sacrifice and the verse says, "On matzot and maror you shall eat it"
Yet, many hagaddot, don't mention the fact that he included the Pesach lamb. So are there various opinions as to what he actually did? What are the opinions based upon?