hello there, your front to rear hub flanges maybe slightly different sizes - as those hubs might be like a campagnolo road hub - those are different flanges
-if you have 184 and 190 and you have 36 of each
36 190's for the front wheel - if you used 184, maybe you'd see some threads
36 184 for the rear = the flange is bigger
-you will find your wheels will be 3 cross = over-over - under
if you are a newbie to wheel building, the ideal spoke length to have, is to have the spoke sitting just shallow of the slot in the nipple, this is so when building the wheel, the spoke naturally pushes the screwdriver out of the slot - you know you are true
-final truing still will not pull the spoke through the head of the nipple
remember - too long of a spoke =i.e. if the spoke comes out of the head of the nipple more than 6ishmm, the nipple will jump off the threads
-also if too short, the threads will show,
note nipple length - there are three lengths, i think the stock length is 14mm - the coloured alloy ones are a few mm longer, some are longer still.
to go into the hub and right on the first spoke, the rim hole next to the valve 'on the left' is 'up'
p.s. just be glad you spotted your error, and are not re-using the spokes, as i just did this with odd spokes, and it drove me around the twist.
also note - availability of spokes, 188mm is commonly available
also on a 7x, remember