I'm sure it will be fine Ian. The "18" is likely to just be an unimportant manufacturering detail - something like "has tin-plated pins", or the kind of packaging it's sold in. The further you get from the main part number, the less important the number tends to be.
You might want to order another couple once you have checked it is working fine in your enlarger - always nice to have a spare or two sitting around ready (he said, having just had to chase around t'internet for a new lamp himself a few weeks ago
).
Have fun, Bob.