Thanks Jan.

The language/culture/format of the date picker is fine, and I know there's a 'YearRange' setting you can use in the jQuery UI date picker to limit the range of dates available to be picked, which would help a little, but not much, so I'm happy to leave the date-picker pop-up as it is.

The issue is when someone types the date into the input field (I need to allow them to type as well as using the jQuery UI picker as the potential range is huge).  Everything works great, except that dates outside of SQL Server's range are accepted as valid by jQuery validation (and Contour's own server-side validation).  Since the validation only checks the format, it's passing; it needs to check the range as well which isn't something it does by default nor even via it's own available methods.

My first thought was just to inject 'min' and 'max' attributes into the date fields via JavaScript, which should make HTML5 validation kick-in.  It does, but unfortunately that conflicts with jQuery validation which assumes those values to be integers rather than dates (perhaps because they're text input fields rather than date input fields?).  So that's a no-go.  What I've done instead is to extend jQuery validate with some custom methods.  So in my main site JavaScript file I now have the following:
 

// Extend jQuery validation with min date method
$.validator.addMethod('mindate', function (v, el, minDate) {
    if (this.optional(el)) {
        return true;
    }
    var curDate = $(el).datepicker('getDate');
    return minDate <= curDate;
}, 'Please specify an appropriate date');

// Extend jQuery validation with max date method
$.validator.addMethod('maxdate', function (v, el, minDate) {
    if (this.optional(el)) {
        return true;
    }
    var curDate = $(el).datepicker('getDate');
    return minDate >= curDate;
}, 'Please specify an appropriate date');



jQuery(document).ready(function () {

    // Apply custom validation rules
    var datePickerField = $('.datepickerfield');
    if(datePickerField.length){
        $('.datepickerfield').rules('add', {
            mindate: new Date(1753, 1, 1), // Min SQL Server date range
            maxdate: new Date(2079, 6, 6) // Max SQL Server smalldatetime range (full date time can go up to 9999)
        });
    }

});

I'm not going to be able to solve the server-side validation but client-side should be good enough for now.  I'll raise a bug in the Contour issue tracker so hopefully the gap in the server-side validation can be plugged.