Adding to cart, but not carrying recordset values in item name or description?

This is the Add to Cart button...

<form name="eCartSMC_1_ATC_<?php echo($rsEDITFORM->getColumnVal("SMCformID")); ?>" method="POST" action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".htmlentities($_SERVER["QUERY_STRING"]):""; ?>">
<input type="hidden" name="eCartSMC_1_ID_Add" value="<?php echo($rsEDITFORM->getColumnVal("SMCformID")); ?>">
<button type="submit" class="btn btn-info" name="eCartSMC_1_ATC" id="eCartSMC_1_ATC">Proceed to Payment <i class="fal fa-shopping-cart"></i></button>
</form>

I've got a hidden field called eCartSMC_1_ID_Add with the form ID value, <?php echo($rsEDITFORM->getColumnVal("SMCformID")); ?>, and this is directing to the health-screening-form-checkout.php page.

My recordset on health-screening-form.php is filtering by $_SESSION['eCartSMC_OrderID'] so perhaps that's why the value doesn't always carry over?

I'm confusing myself, as I type here.

Would a solution be to change my recordset to filter by $_SESSION['eCartSMC_OrderID'] OR $_POST['eCartSMC_OrderID']?
Is the Add to Cart behaviour event even a POST though?

Urggh. My brain is hurting.
Are you free to set up this IPN PayPal thing tomorrow, Thursday or Friday this week and perhaps we could iron out thigns like this whilst we're at it?

Cheers.
NJ