I can confirm that. On the TI-83, many of the TI-BASIC tokens contained lowercase characters which couldn't be typed at all - you could only type uppercase letters on the keyboard. (There were a few lowercase letters available as tokens for special purposes, but it wasn't a full set.)
Interestingly, you could print tokens in strings - e.g. you could Disp "Disp ".
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I can confirm that. On the TI-83, many of the TI-BASIC tokens contained lowercase characters which couldn't be typed at all - you could only type uppercase letters on the keyboard. (There were a few lowercase letters available as tokens for special purposes, but it wasn't a full set.)
Interestingly, you could print tokens in strings - e.g. you could Disp "Disp ".
The 83+ let you type the full set of lowerchase chars as well, but they used 2x as many bytes per character for storage.
There's actually a hidden lowercase feature, you can use an assembly program to enable it.