Saver Business Class fare. Like Saver coach fares, no other discounts apply.
Maybe so - but with the saver (coach) fare there is a "Fare Alert" flag to notify you that the senior discount does not apply and the regular (saver) adult fare is shown. In this case there is no "Fare Alert" flag and the regular adult fare is definitely not shown. Indeed, you are actually paying *MORE* than the regular adult fare so it is not the case that the senior discount simply does not apply.
The Amtrak.com booking page leaves a lot to be desired. This is one of those failings.
$49 is the "Saver Fare" and, as mentioned before, program discounts like AAA or senior do not apply. The Saver fare is also not refundable. The Adult refundable Value fare is $89. With a Saver fare available, the Business Class fare is $94 which is the $49 Saver Fare plus a $45 up charge for Business Class. So far, so good.
Now, when you ask for the Senior Fare (15% discount), things get a little weird. The Saver fare of $49 is still shown but is flagged as not discounted. The Value fare is now discounted by 15% and is $75.65. Asking for the senior discount, the Business Class option assumes you don't want the Saver fare even though it is shown. So, it uses the discounted Value fare ($75.65) as the base, adds the $45 Business Class up charge, and comes up with $120.65.
So, basically, if you want the Saver fare in Business Class for $94, you have to book as an "Adult." If you want a senior discounted Business Class fare (more than Saver, but refundable), then you can book as a senior