I wanted to ask about how to read machine code as assembly code. I have only done convertions that looks like this

001000 00001 00000 0000000000000100   -- addi $r0, $r1, 0x0004

or R-type instruction like this

000000 00000 00001 00010 00000 100000 -- add  $r2, $r0, $r1

for example. But now I’ve come across some instructions that looks like this

001000 10001 10000 0000000000000101   -- addi $s0, $s1, 5

and

001000 10011 01000 1111111111110100   -- addi $t0, $s3, –12

I know that for addi instruction it is addi target_reg, source_reg, imm and I assume they write $t and $s here because it is the target and source reg, but I don’t understand why they are red differently then the once I gave example on first.
If I would have red the machine code for the lw instruction for example, I would have written it as

addi $t16, $s17, 5

and

addi $t8, $s19, -12

Could someone help me understand what is wrong with this way of converting these code snippets where it is not wrong in my first examples.