הָאוֹמֵר לְעַבְדּוֹ, צֵא וּשְׁחֹט עָלַי אֶת הַפֶּסַח, שָׁחַט גְּדִי, יֹאכַל. שָׁחַט טָלֶה, יֹאכַל. שָׁחַט גְּדִי וְטָלֶה, יֹאכַל מִן הָרִאשׁוֹן.
שָׁכַח מָה אָמַר לוֹ רַבּוֹ, כֵּיצַד יַעֲשֶׂה, יִשְׁחַט טָלֶה וּגְדִי וְיֹאמַר, אִם גְּדִי אָמַר לִי רַבִּי, גְּדִי שֶׁלּוֹ וְטָלֶה שֶׁלִּי. וְאִם טָלֶה אָמַר לִי רַבִּי, הַטָּלֶה שֶׁלּוֹ וּגְדִי שֶׁלִּי. שָׁכַח רַבּוֹ מָה אָמַר לוֹ, שְׁנֵיהֶם יֵצְאוּ לְבֵית הַשְּׂרֵפָה, וּפְטוּרִין מִלַּעֲשׂוֹת פֶּסַח שֵׁנִי:
If someone says to his servant "Shecht (slaughter) a korban Pesach (Paschal sacrifice) for me": if he shechts a goat, the master should eat it, if he shechts a sheep, the master should eat it. If he shechts both, the master should eat the first one.
If he forgets what the master said, he should shecht a sheep and a goat and say "If my master told me to shecht a goat, the goat is his and the sheep is mine. If my master told me to shecht a sheep, the sheep is his and the goat is mine." If the master also forgets what he said, both animals get burned, and neither of them have to do Pesach Sheini.
It seems that forgetting which animal one was sent to bring is common enough to be worth mentioning and ruling on.
Pesachim 8:6 lists several people who are probably going to be able to eat the Pesach that night, but who have a high probability of being disqualified. It rules that:
הָאוֹנֵן, וְהַמְפַקֵּחַ אֶת הַגַּל, וְכֵן מִי שֶׁהִבְטִיחוּהוּ לְהוֹצִיאוֹ מִבֵּית הָאֲסוּרִים, וְהַחוֹלֶה וְהַזָּקֵן שֶׁהֵן יְכוֹלִין לֶאֱכֹל כַּזַּיִת, שׁוֹחֲטִין עֲלֵיהֶן. עַל כֻּלָּן אֵין שׁוֹחֲטִין עֲלֵיהֶן בִּפְנֵי עַצְמָן, שֶׁמָּא יָבִיאוּ אֶת הַפֶּסַח לִידֵי פְסוּל.
An onein (who's close relatve died that day), a search and rescue worker, someone who was promised to be let out of jail, or a sick or old person who can eat a kezayis, we can shecht a korban Pesach for them. In all of these cases, we don't shecht a korban Pesach for them alone, so that they don't disqualify it.
My question: Why not recommend that the servant in Mishnah Pesachim 8,2 do the same thing as in 8,6? That is, he should find at least two other people willing to cooperate, and register one on the goat and one on the sheep unconditionally. That way, even if the master forgets what he said, not one of the korbanos would be disqualified and burned.