@pen one in each iteration of the forEach you are just overwriting the field value with the current result. You need to build the value and set it once outside of the loop. Something like

var licenseNumbersList = '';

for(var i=0; i < pagedData.pageRanges.length; i++ ) {
	var currentPage = pagedData.fetch(i);
	currentPage.data.forEach(function(result) {
		var licenseNumbers = result.getValue({ name: "custrecord_license_number", join: "CUSTRECORD230", summary: "GROUP"});
		console.log("License Numbers are " + licenseNumbers)
		licenseNumbersList = licenseNumbersList + "\n" + licenseNumbers;
	});
}

recCurrent.setValue({ fieldId: 'custbody_all_license_numbers', value: licenseNumbersList});

Thanks @michoel! It worked!