changed the logic to show the more button from using a count to using an api provided flag.

yammer.events.js

(function () {
    
    
    var activeTabClass = "yj-active-tab";
    var eventsLink;
    var lastId;
    var column = yam.$('#column-two');        
    var mainColumn = column.find('.yj-main-content').empty();
    var eventList = yam.$("<div id='event-list'>").appendTo(mainColumn);
    eventList.click(function () { eventList.empty(); }); //empty the content if an event item is clicked.
    var loading = yam.$('<div id="notificationMenuSpinner" class="yj-spinner-loading-container"><div class="yj-spinner-loading">Loading...</div></div>').appendTo(mainColumn);
    var moreButtonText = "<a id='moreButton' href='javascript:;'><h2>more</h2></a>";
    
    
    function fetchResults() {
        var url = 'https://www.yammer.com/api/v1/messages/attachments/3.json?filter=event&threaded=true&sort_by=created_at&reverse=true';
        if(lastId) {
            url = url + '&older_than=' + lastId;
        }
        loading.show();
        
        mainColumn.find('#moreButton').remove();
        //fetch results
        yam.$.ajax({ 
            url: url, 
            success: function (msgs) {
                if(!msgs.messages) {
                    return;
                }
                var promises = [];
                msgs.messages.forEach(function (msg) {
                    promises.push(yam.$.get(msg.attachments[0].inline_url).done(function (text) {
                         msg.rendered_content = text;
                    }));
                });
                yam.$.when.apply(yam.$, promises).done(function () {
                    msgs.messages.forEach(function (msg) {
                       eventList.append(msg.rendered_content); 
                       eventList.append('<br />');
                    });
                    if(msgs.meta.older_available) {
                        mainColumn.append(moreButtonText).click(fetchResults);                        
                    }
                    loading.hide();
                });
                lastId = msgs.messages[msgs.messages.length - 1].id;
                console.log("message count", msgs.messages.length);
            },
            failure: function () {
                console.log(arguments);
                alert("error retrieving events. see console for details");
            }
        });  
    }
    if(!yam.$('#events-tab').length) {
        eventsLink = yam.$('<li class="yj-header-menu-item yj-header-list-section-border" id="events-tab" data-yj-tabname="events">' +
        '<a href="#/events" class="link has-left-border has-right-border" data-action="events" title="Events">' +
          '<span class="yamicon yamicon-yam-spittle yamicon-regular yj-header-img"></span>' +
          '<span class="text">Events</span>' +
        '</a>' +
     '</li>').appendTo('#header-jewels');
    
        yam.$('#header-jewels').click(function (ev) {
            //clean up content if user switches
            if(yam.$(ev.target).parents('#events-tab').length === 0) {
                mainColumn.empty();
                eventList.empty();    
                lastId = null;
            }
        });
        //set active tab
        yam.$('#header-jewels').children().removeClass(activeTabClass);
        eventsLink.addClass(activeTabClass);
        
        eventsLink.click(function () {
            fetchResults();
        });
        
        //prepare column content

        column.find('.page-header-container').html('<div class="page-header-container"><div class="page-header" style="display: block;"><div><h2 class="header-content">Events</h2></div></div></div></div>');
        fetchResults();
    } else {
        yam.$('#events-tab').remove();
        loading.remove();
    }

})();


            /* 
            {
        "id": 344134817,
        "sender_id": 1507340463,
        "replied_to_id": null,
        "created_at": "2013/11/22 05:40:59 +0000",
        "network_id": 10580,
        "message_type": "update",
        "sender_type": "user",
        "url": "https://www.yammer.com/api/v1/messages/344134817",
        "web_url": "https://www.yammer.com/monex.co.jp/messages/344134817",
        "group_id": 3243699,
        "body": {
            "parsed": "(See attached Event)",
            "plain": "",
            "rich": "(See attached Event)"
        },
        "thread_id": 344134817,
        "client_type": "Web",
        "client_url": "https://www.yammer.com/",
        "system_message": false,
        "direct_message": false,
        "chat_client_sequence": null,
        "content_excerpt": "",
        "language": "en",
        "notified_user_ids": [],
        "privacy": "public",
        "attachments": [
            {
                "id": 11651849,
                "type": "ymodule",
                "name": "Events: Bo-Nen-Kai 2013, Chicago",
                "url": "https://www.yammer.com/api/v1/ymodules/11651849",
                "web_url": "https://www.yammer.com/monex.co.jp/messages/344134817",
                "inline_url": "https://www.yammer.com/monex.co.jp/ymodule/11651849/inline",
                "ymodule": {
                    "app_id": "events",
                    "icon_url": "https://mug0.assets-yammer.com/mugshot/images/16x16/3rd_party.png"
                }
            }
        ],
        "liked_by": {
            "count": 0,
            "names": []
        }
    } 
    */